Wheel-state obtaining apparatus, and vehicle-state obtaining apparatus

ABSTRACT

A wheel-state obtaining apparatus for a vehicle, including wheel-side devices ( 10 - 16 ) each having an air pressure sensor ( 32 ) for detecting an air pressure of a wheel tire of the vehicle, and a body-side device ( 18 ) having receiver antennas ( 20 - 26 ) and arranged to receive wheel-side information from the wheel-side devices through the receiver antennas and extract air-pressure information representative of the detected air pressure, that is, detected-air-pressure information, and wherein the body-side device includes an estimating portion ( 54 ) which is operable, in the event of a failure of any of the receiver antennas to receive the wheel-side information, to estimate the tire air pressure on the basis of detected speeds of the wheel, and obtain estimated-air-pressure information representative of the estimated air pressure. Thus, the wheel-state obtaining apparatus is capable of obtaining information on the air pressure even in the event of a failure of the receiver antennas ( 20 - 26 ) to receive the wheel-side information.

TECHNICAL FIELD

The present invention relates to a vehicle-state obtaining apparatusarranged to obtain information indicative of a state of a vehicle

BACKGROUND ART

JP-A-2000-238515 describes a wheel-state obtaining apparatus, whichincludes wheel-side devices respectively provided on a plurality ofwheels of a vehicle, and a body-side device disposed on a body of thevehicle, and wherein wheel-side information is transmitted from thewheel-side devices to the body-side device, so that informationindicative of the states of the wheels is obtained. Each of thewheel-side devices includes an air-pressure detecting device operable todetect an air pressure of a tire of the corresponding wheel, and atransmitter device operable to transmit information indicative orrepresentative of the air pressure detected by the air-pressuredetecting device, while the body-side device includes a receiver deviceoperable to receive the information transmitted from the wheel-sidedevices, and an air-pressure-information obtaining device operable toextract the information representative of the air pressure, from thewheel-side information received from the wheel-side devices. Eachwheel-side device is arranged to transmit the wheel-side information ata predetermined first time interval while the detected tire air pressureis changing at a relatively low rate, and at a predetermined second timeinterval shorter than the first time interval, while the tire airpressure is changing at a relatively high rate. Accordingly, thebody-side device receives the wheel-side information at the first timeinterval while the tire air pressure of each wheel is changing at therelatively low rate, and at the second time interval while the tire airpressure of the wheel is changing at the relatively high rate.

In the wheel-state obtaining apparatus described above, the wheel-sideinformation including the information representative or indicative ofthe air pressure is transmitted from each wheel-side device, and thetransmitted information is received by the body-side device, and theinformation representative of the air pressure is extracted from thereceived wheel-side information. Where the body-side device cannotreceive the wheel-side information due to a noise, for example, thewheel-state obtaining apparatus cannot obtain the air pressureinformation.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to make it possibleto obtain, with a higher degree of stability, information indicative ofa state of a vehicle, such as a tire air pressure of each wheel, byusing a plurality of information obtaining devices.

This object may be achieved according to any one of the following modesof the present invention. Each of these modes is numbered like theappended claims and depends from the other mode or modes, whereappropriate, for easier understanding of the technical featuresdisclosed in the present specification. It is to be understood that thepresent invention is not limited to the technical features or anycombinations thereof which will be described. It is to be furtherunderstood that a plurality of elements or features included in any oneof the following modes of the invention are not necessarily provided alltogether, and that the invention may be embodied with selected at leastone of the elements or features described with respect to the same mode.

(1) A wheel-state obtaining apparatus comprising:

-   -   a wheel-side device provided for each of at least one of a        plurality of wheels of a vehicle and including a        first-wheel-state detecting device operable to detect a first        state of the corresponding wheel; and    -   a body-side device disposed on a body of the vehicle and        including (a) a detected-information obtaining device operable        to obtain detected information representative of the first state        of the above-indicated corresponding wheel detected by the        first-wheel-state detecting device, (b) a vehicle-state        detecting device operable to detect a state of the vehicle, (c)        an estimated-information obtaining device operable to estimate        the first state of the above-indicated corresponding wheel on        the basis of at least the state of the vehicle detected by the        vehicle-state detecting device, and obtain estimated information        representative of the estimated first state, and (d) a        determining device operable to determine one of the detected        information and the estimated information, as wheel-state        information representative of the first state of the        above-indicated corresponding wheel.

The wheel-state obtaining apparatus according to the above mode (1) isprovided with the detected-information obtaining device and theestimated-information obtaining device, as devices for obtaininginformation representative of one state of the vehicle. Accordingly,even when one of the detected-information and estimated-informationobtaining devices is not able to obtain the corresponding detected orestimated information, the present apparatus is capable of obtaining theother information representative of the state of the wheel in question.

In the present wheel-state obtaining apparatus, one of the estimatedinformation and the detected information is determined as thewheel-state information representative of the first state of the wheel.That is, the wheel-state information representative of the first stateof the wheel in question may be obtained as either the estimatedinformation or the detected information. In other words, the first stateof the wheel in question is directly detected, or estimated (indirectlyobtained).

The determining device may be arranged to select one of the estimatedinformation and the detected information as the wheel-state information,according to a predetermined rule. Alternatively, the determining devicemay be arranged to normally select a predetermined one of the estimatedinformation and the detected information, and select the otherinformation only when a predetermined condition is satisfied. Forinstance, the determining device may be arranged to alternately selectthe estimated information and the detected information, or repeatedlyuse one of the estimated information and the detected information fortwo or more cycles of control once that information has been selected.Alternatively, the determining device may be arranged to compare thefirst state of the wheel represented by the estimated information andthe first state represented by the detected information, with eachother, and select the estimated or detected information which must begiven to the vehicle operator with higher priority. Where the firststate of the wheel in question is represented by a quantity, thedetermining device may be arranged to select the estimated or detectedinformation whose quantity deviates from an optimum value by a largeramount. Further, the determining device may be arranged to normallyselect a predetermined one of the detected information and the estimatedinformation, and select the other information where the selection of thepredetermined one information would cause an undesirable result, orselect a predetermined one of the detected and estimated information, inprinciple, and select the other information where the selection of theother information is more desirable. For example, the determining deviceselects, as the wheel-state information, the detected information whenthe first state of the wheel has been detected by the first-statedetecting device, and the estimated information when the first state hasnot been detected by the first-state detecting device. Alternatively,the determining device selects, in principle, the detected informationwhen the first state of the wheel has been detected, but selects theestimated information if a predetermined condition is satisfied evenwhen the first state has been detected. Conversely, the determiningdevice may be arranged to normally select the estimated information, andselect the detected information if the accuracy of the estimatedinformation is lower than a predetermined lower limit. The conditionused to select one of the estimated information and the detectedinformation will be described in detail.

The first-wheel-state detecting device, which is operable to detect thefirst state of the wheel, may be arranged to detect a first-wheel-statequantity representative of the first state of the wheel, or to indicatewhether the first state of the wheel is optimum (for example, whetherthe first-wheel-state quantity is held within a predetermined optimumrange, or larger than a predetermined lower limit). Where the firststate of the wheel is an air pressure of a tire of the wheel inquestion, for instance, the first-wheel-state detecting device may be anair-pressure detecting device operable to detect a value of the airpressure of the wheel tire, or alternatively a pressure switch operableto determine whether the air pressure is normal (whether the airpressure is held within a predetermined optimum range). Thus, the firststate of the wheel may be represented by a physical quantity, or byinformation indicating whether the physical quantity is optimum or not.The first state of the wheel is interpreted to comprehend those physicalquantity and information. Similar interpretation applies to the firststate estimated by the estimated-information obtaining device, and thestate of the vehicle detected by the vehicle-state detecting device.

The estimated-information obtaining device, which is arranged toestimate the first state of the wheel on the basis of the state of thevehicle, may be arranged to estimate the first state of the wheel on thebasis of only one state of the vehicle or a plurality of states of thevehicle. Where the first state of the wheel is a temperature of a tireof the wheel, the estimated-information obtaining device may be arrangedto estimate the tire temperature or overheating of the tire, on thebasis of only a total or cumulative running time of the vehicle after anignition switch of the vehicle has been turned from its OFF state to itsON state, or alternatively, on the basis of not only the cumulativerunning time, but also an ambient temperature of the vehicle and a loadacting on the tire. Further, the estimated value of the first state ofthe wheel may be obtained on the basis of the detected value of thefirst state of the wheel represented by the detected informationobtained by the detected-information obtained device. Where the firststate of the wheel is estimated on the basis of the latest detectedvalue, as described below, for example, a final estimated value of thefirst state of the wheel may be obtained on the basis of the detectedvalue and a provisional estimated value of the first state, and weightsgiven to these detected and provisional estimated values. For instance,the final estimated value z may be estimated according to the followingequation:z=xα+y(1−α)

In the above equation, “x” represents the detected value, and “y”represents the provisional estimated value, while “α” (0≦α<1) representsthe weight given to the detected value x.

The vehicle-state detecting device may be arranged to detect a secondstate of the wheel other than the first state, or an operating state ofa device of the vehicle (a device installed or built in the vehicle,such as a drive system, a power-transmission system, a braking system, asteering system, and a suspension system), an operating state of amember manually operated by a driver or operator of the vehicle (such asa steering member, a brake operating member, and an acceleratingmember), or a running state of the vehicle, for example. On the basis ofthe detected operating state of the device of the vehicle or of themanually operated member or the detected running state of the vehicle,it is possible to estimate the state of the wheel (for example, brakingstate, driving state or steering state of the wheel, forces acting onthe wheel, air pressure or temperature of the tire, or rotating state ofthe wheel). The above-indicated parameters are suitably used to estimatethe first state of the wheel.

(2) A wheel-state obtaining apparatus according to the above mode (1),wherein the determining device includes an individually determiningportion operable for each of the plurality of wheel, independently ofeach other, such that one of the detected information and the estimatedinformation is determined as the wheel-state information for each of theplurality of wheels.

(3) A wheel-state obtaining apparatus according to the above mode (1),wherein the determining device includes an overall determining portionoperable for all of the plurality of wheels, such that one of thedetected information and the estimated information is determined as thewheel-state information, commonly for all of the plurality of wheels.

The determining device may be arranged to select one of the detectedinformation and the estimated information, for each of the plurality ofwheels, independently of each other, or select the detected or estimatedinformation commonly for all of the wheels. For example, the determiningdevice is arranged such that a determination as to whether apredetermined condition for selecting the detected or estimatedinformation is satisfied is effected for each of the wheels,independently of each other, or alternatively effected for the pluralityof wheels as a whole. Further, it is possible to select one of thedetected information and the estimated information, for each of two ormore groups of the wheels, each group consisting of at least one wheel.

(4) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(3), wherein the determining device includes adetection-failure estimated-information determining portion operable todetermine the detected information as the wheel-state information whenthe first state of the above-indicted corresponding wheel has beendetected by the first-wheel-state detecting device, and determine theestimated information as the wheel-state information when the firststate has not been detected by the first-wheel-state detecting device.

In the wheel-state obtaining apparatus according to the above mode (4),the detected information is selected, in principle, as the wheel-stateinformation. When the first state of the wheel has been detected by thefirst-wheel-state detecting device, the first state of the wheel isobtained on the basis of the detected information, for example. Thefirst state of the wheel represented by the detected information wasdirectly detected by the first-wheel-state detecting device, and istherefore more accurate than the first state represented by theestimated information. Accordingly, the first state of the wheel can bemore accurately obtained according to the above mode (4), than where thefirst state is always obtained on the basis of the estimatedinformation. The detected information may be referred to as “directlyobtained information”, as distinguished from the estimated informationwhich may be referred to as “indirectly obtained information”.

When the first state of the wheel in question has not been detected bythe first-wheel-state detecting device, the determining devicedetermines the estimated information as the wheel-state information.Thus, the first state of the wheel can be obtained even when the firststate has not been detected by the first-wheel-state detecting device.Namely, the first state is necessarily obtained at a predeterminedtiming of detection of the first state. In the present wheel-stateobtaining apparatus, the estimated-information obtaining device may bearranged to obtain the estimated information while thedetected-information obtaining apparatus is not in operation to obtainthe detected information. In this case, the information representativeof the first state of the wheel can be obtained at a relatively shorttime interval.

(5) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(4), wherein the wheel-side device further includes (a) awheel-side-information transmitting device operable to transmit, in awireless fashion, wheel-side information representative of the firststate of the above-indicated corresponding wheel detected by thefirst-wheel-state detecting device, and (b) an electric power sourceoperable to supply the wheel-side-information transmitting device andthe first-wheel-state detecting device with an electric energy, and thebody-side device further includes a receiving device operable to receivethe wheel-side information transmitted from the wheel-side device, thedetected-information obtaining device including a detected-informationextracting portion operable to extract from the wheel-side informationthe detected information representative of the first state of thecorresponding wheel.

The wheel-side-information transmitting device of the wheel-side devicemay be arranged to transmit the wheel-side information at apredetermined time interval, namely, periodically, or non-periodically,for instance, when the transmission of the information representative ofthe first state of the wheel is required, or when the first-wheel-statedetecting device has a predetermined output amount or state. That is,the wheel-side-information transmitting device may transmit thewheel-side information in response to a request received from thebody-side device, or according to a condition of the wheel-side device.Where the wheel-side information is transmitted periodically, thetransmission time interval or frequency may be changed as needed, as inthe prior art apparatus.

The wheel-side information transmitted from the wheel-side-informationtransmitting device of the wheel-side device is received by thereceiving device of the body-side device, and the informationrepresentative of the first state of the wheel is extracted from thewheel-side information received by the receiving device, to obtain thedetected information. Thus, the detected information is obtained byextraction from the wheel-side information received by the receivingdevice, and may therefore be referred to as “received information”.Since the detected information is transmitted in a wireless orradio-communication fashion, it may be referred to as “radio-transmittedinformation” or “wireless-transmitted information.

On the other hand, the vehicle-state detecting device is connectedthrough a signal line to the estimated-information obtaining device, andthe information representative of the state of the vehicle detected bythe vehicle-state detecting device is supplied through the signal lineto the estimated-information obtaining device, so that the first stateof the wheel is estimated on the basis of the information received bythe estimated-information obtaining device. In this respect, theestimated information may be referred to as“cable-transmission-dependent information” or“wire-transmission-dependent information”.

The electric power source provided in the wheel-side device is differentand separate from an electric power source provided in the body-sidedevice, and may be independent of, or dependent on the electric powersource provided in the body-side device. The electric power source inthe wheel-side device may be a power source not having an electricitygenerating function or a charging function, that is, may be a battery.However, the electric power source in the wheel-side device may have atleast one of the electricity generating function and the chargingfunction. For instance, the electric power source in the wheel-sidedevice may be provided with an electric generator operated by a rotarymotion of the wheel, for example, an electric generator ofelectromagnetic induction type, or an electric generator of mechanicalmotion type. Alternatively, the electric power source has a function ofgenerating electricity utilizing a contact of the tire with the roadsurface (for example, by utilizing piezoelectric elements), or has solarcells disposed on the surface of the wheel. Further alternatively, theelectric power source in the wheel-side device may be charged with anelectric energy supplied from the body-side device by transmission of ahigh-frequency wave.

(6) A wheel-state obtaining apparatus according to the above mode (5),wherein the determining device includes a reception-condition-dependentdetermining portion operable to determine one of the detectedinformation and the estimated information as the wheel-stateinformation, on the basis of a condition of reception of the wheel-sideinformation by the receiving device.

The determining device may be arranged to determine one of the detectedinformation and the estimated information as the wheel-stateinformation, depending upon whether the wheel-side information has beennormally received by the receiving device, or whether the receivingdevice has difficulty in receiving the wheel-side information (forexample, whether a ratio of reception of the wheel-side information ishigher than a predetermined threshold, or whether the receiving deviceis normal or abnormal).

(7) A wheel-state obtaining apparatus according to the above mode (5) or(6), wherein the determining device includes a determining portionoperable to determine the estimated information as the wheel-stateinformation when the wheel-side information has not been normallyreceived by the receiving device, and determine the detected informationas the wheel-state information when the wheel-side information has beennormally received by the receiving device.

(8) A wheel-state obtaining apparatus according to the above mode (7),wherein the determining portion determines the estimated information asthe wheel-state information when the wheel-side information received bythe receiving device is abnormal, and determines the estimatedinformation as the wheel-state information when the wheel-stateinformation received by the receiving device is normal.

In the wheel-state obtaining apparatus according to the above mode (7),the estimated information is determined as the wheel-state informationwhen the wheel-side information has not been received by the receivingdevice. The wheel-side information is not received by the receivingdevice (a) even when the receiving device is normal, where thewheel-side information is not transmitted from the wheel-side device dueto an abnormality of the wheel-side device, or during a period in whichthe wheel-side information is not transmitted from the wheel-side devicewhich is arranged to transmit the wheel-side information at apredetermined interval, or where the wheel-side information is notreceived by the receiving device due to a noise included in thewheel-side information, or (b) when the wheel-side information is notreceived by the receiving device due to an abnormality of the receivingdevice. The case (a) includes: a partial loss of the wheel-sideinformation as received by the receiving device and a consequent failureof the detected-information extracting portion to extract the detectedinformation representative of the first state of the wheel; abnormalityof the wheel-side information received by the receiving device. Wherethe wheel-side device is arranged to transmit the wheel-side informationat the predetermined interval, the above-indicated period in which thewheel-side information is not transmitted is a period from the moment ofthe last transmission of the wheel-side information to the moment of thenext transmission. The interval of transmission of the wheel-sideinformation from the wheel-side-information transmitting device of thewheel-side device may be considered to be equal to the interval ofreception of the wheel-side information by the receiving device of thebody-side device, under a predetermined condition. The interval ofreception is a period from the moment of the last reception of thewheel-side information to the moment of the next reception.

Where the wheel-side information is transmitted from the wheel-sidedevice periodically at a predetermined interval, and the estimatedinformation is obtained between the moments of transmission, theestimated information representative of the first state of the wheel isobtained at a relatively short time interval by the body-side device,even where the transmission interval is relatively long. In other words,the transmission interval of the wheel-side device may be prolonged, andthe amount of electric energy required to transmit the wheel-sideinformation can be accordingly reduced. Accordingly, the arrangement toobtain the estimated information at an interval shorter than thetransmission interval is particularly advantageous, where the electricpower source is a battery, since the service life of the battery can beprolonged.

(9) A wheel-state obtaining apparatus according to any one of the abovemodes (5)-(8), wherein the determining device includes areception-failure estimated-information determining portion operable todetermine the estimated information as the wheel-state information whenthe wheel-side information has not been received by the receivingdevice, at a predetermined timing of reception of the wheel-sideinformation by the receiving device.

(10) A wheel-state obtaining apparatus according to the above mode (9),wherein the wheel-side-information transmitting device includes aperiodically transmitting portion operable to transmit the wheel-sideinformation at a predetermined interval of transmission.

Where the timing of reception of the wheel-side information by thereceiving device is known to the body-side device, the reception-failuredetermining portion of the determining device determines the estimatedinformation as the wheel-side information when the wheel-sideinformation has not been received by the receiving device at thepredetermined timing of reception, or within a predetermined periodafter the predetermined timing or reception. Where thewheel-side-information transmitting device of the wheel-side device isarranged to transmit the wheel-side information at a predeterminedinterval of transmission as in the apparatus according to the above mode(10), the timing of reception of the wheel-side information is known tothe receiving device.

The estimated information is determined as the wheel-state informationwhen the wheel-side information has not been transmitted at thepredetermined timing of transmission, due to an abnormality of thewheel-side device, so that the wheel-side information has not beenreceived by the receiving device, or when the wheel-side information hasnot been received by the receiving device due to an abnormality of thereceiving device.

The wheel-state obtaining apparatus according to the above modes (9) and(10) is advantageous in that the first state of the wheel can beobtained even where the wheel-side information is not or cannot bereceived by the receiving device.

Where the wheel-side device is operable to transmit the wheel-sideinformation at a selected one of a plurality of different transmissionintervals, as in the prior art apparatus, the receiving device ispreferably arranged to receive the wheel-side information at thereception interval which is equal to the shortest transmission interval.

(11) A wheel-state obtaining apparatus according to any one of the abovemodes (5)-(10), wherein the wheel-side-information transmitting deviceincludes a periodically transmitting portion operable to transmit thewheel-side information at a predetermined interval of transmission, andthe estimated-information obtaining device is operable to obtain theestimated information during a predetermined interval of reception ofthe wheel-side information by the receiving device.

In the wheel-state obtaining apparatus according to the above mode (11),the firs state of the wheel is estimated during the predeterminedinterval of reception of the wheel-side information, so that theestimated information is obtained at least once during each period ofreception of the wheel-side information. The estimated information maybe obtained only once or a plurality of times during each period ofreception of the wheel-side device by the receiving device. During eachperiod of reception, the estimated information may be obtained at apredetermined interval, or in response to a signal received form anexternal device.

(12) A wheel-state obtaining apparatus according to any one of the abovemodes (5)-(11), wherein the determining device includes areception-condition determining portion operable to determine whether aratio of reception of the wheel-side information by the receiving deviceis relatively high or low, and a reception-condition-dependentdetermining portion operable to determine the detected information asthe wheel-state information when the reception-condition determiningportion determines that the ratio of reception is relatively high, anddetermine the estimated information as the wheel-state information whenthe reception-condition determining portion determines that the ratio ofreception is relatively low.

The ratio of reception of the wheel-side information by the receivingdevice is considered to be relatively low in a condition in which thereis a high possibility of generation of a noise. The determination as towhether the possibility of generation of the noise can be effected onthe basis of the running state of the vehicle. During straight runningof the vehicle at an almost constant speed, the possibility ofgeneration of the noise is lower, and the ratio of reception of thewheel-side information by the receiving device is higher, than duringacceleration or deceleration of the vehicle. During running of thevehicle on a relatively flat (non-undulated) or good roadway, thepossibility of generation of the noise is lower, and the ratio ofreception of the wheel-side information is higher, than during runningof the vehicle on a bad roadway.

(13) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(12), wherein the vehicle-state detecting device includes asecond-wheel-state detecting device operable to detect a second state ofeach of at least one of the plurality of wheels, the second state beingdifferent from the first state.

In the wheel-state obtaining apparatus according to the above mode (13),the first state of the wheel in question (wheel whose first state isestimated) is estimated on the basis of the second state of the wheel inquestion, or on the basis of the second state of a plurality of wheelsincluding the wheel in question. Where the first state is an airpressure of the tire of the wheel in question, while the second state isa rotating speed, for example, the tire air pressure of the wheel inquestion may be estimated on the basis of a plurality of values of therotating speed of the wheel in question. It is known that there is apredetermined relationship between an amount of change of a springconstant of the wheel tire and an amount of change of the air pressureof the tire. The amount of change of the spring constant is obtained onthe basis of the two or more values of the rotating speed of the wheelin question. For example, the tire air pressure may be obtained on thebasis of a resonance frequency obtained by frequency analysis of the twoor more speed values of the wheel in question, and a predeterminedrelationship between the amount of change of the resonance frequency andthe amount of change of the spring constant of the tire. Alternatively,the tire air pressure may be obtained by using an external disturbanceobserver. Thus, the air pressure of the tire may be estimated on thebasis of the resonance frequency or by using the external disturbanceobserver.

Where the rotating speed of the wheel in question is excessively higherthan an average value of the rotating speeds of a plurality of wheelsincluding the wheel in question, the tire air pressure of the wheel inquestion is considered to be abnormal.

The first state of the wheel in question may be estimated on the basisof only the second state, or on the basis of not only the second statebut also any additional physical value or values. For example, the firststate may be estimated by taking into account any other state of thevehicle, such as a third state of the wheel different from the secondstate, or a driving state of the vehicle, or the first state of theother wheel or wheels. The third state may be that of the wheel inquestion or that of any other wheel or wheels. Informationrepresentative of the third state may be transmitted from the wheel-sidedevice, by radio communication with the body-side device, together withor independently of the information representative of the first state,or supplied directly to the body-side device through a signal line, forexample.

Where the tire air pressure as the first state of the wheel in questionis estimated on the basis of the rotating speed of the wheel as itssecond state, the estimation may be made by taking account of atemperature of the tire as the third state of the wheel in question, orthe running speed of the vehicle as another state of the vehicle, forexample. JP-A-2000-238516 describes that the tire air pressure of thewheel in question estimated on the basis of a plurality of values of therotating speed of the wheel is influenced by the temperature of the tireand the running speed of the vehicle. The tire air pressure of the wheelin question may be estimated by taking account of the tire air pressureof any other wheel or wheels. For instance, the tire air pressure of thewheel in question may be estimated on the basis of the angularvelocities of the wheel in question and any other wheel, and the tireair pressure or pressures of the other wheel or wheels. The effectiveradius of a tire decreases with a decrease in the tire air pressure, sothat the angular velocity of the wheel increases with the decrease ofthe tire air pressure. In this case, the estimation of the tire airpressure is based on the dynamic load radius of the wheel.

(14) A wheel-state obtaining apparatus according to any one of the abovemodes (5)-(13), wherein the estimated-information obtaining deviceincludes a detected-state estimating portion operable to estimate thefirst state of the above-indicated corresponding wheel after lastreception of the wheel-side information by the receiving device, on thebasis of at least the first state of the above-indicated correspondingwheel represented by the wheel-side information received last by thereceiving device.

In the wheel-state obtaining apparatus according to the above mode (14),the first state of the wheel in question represented by the lastobtained detected information is utilized to estimate the first state.The accuracy of estimation of the first state can be improved where thefirst state estimated on the basis of the state of the vehicle isobtained by taking account of the first state which was directlydetected last.

The first state represented by the detected information (detected firststate) may be coincident with the first state estimated on the basis ofthe state of the vehicle (estimated first state), under some condition.However, the estimated first state may be different from the detectedfirst state. To reduce this difference, the estimated first state isestimted on the basis of the last detected value of the first state.

(15) A wheel-state obtaining apparatus according to the above mode (14),wherein the vehicle-state detecting device includes a second-wheel-statedetecting device operable to detect a second state of each of at leastone of the plurality of wheels, the second state being different fromthe first state, and the detected-state estimating estimates the firststate of the above-indicated corresponding wheel, on the basis of thefirst state represented by the wheel-side information received last bythe receiving device, and the second state detected by thesecond-wheel-state detecting device.

In the wheel-state obtaining apparatus according to the above mode (15),the first state of the wheel in question which has been detected last bythe first-wheel-state detecting device to obtain the last detectedinformation is estimated on the basis of the second state of the wheelin question and the first state represented by the last detectedinformation.

(16) A wheel-state obtaining apparatus according to any one of the abovemodes (13)-(15), wherein the detected-state estimating portion includesan estimating portion operable to estimate the first state of thecorresponding wheel, according to a predetermined rule on the basis ofthe second state of each of the above-indicated at least one of theplurality of wheels detected by the second-wheel-state detecting device,and a rule-changing portion operable to change the predetermined rule onthe basis of the first state of the above-indicated corresponding wheelrepresented by the detected information which has been extracted by thedetected-information obtaining device from the last received wheel-sideinformation.

The accuracy of estimation of the first state of the wheel in questioncan be improved by changing the rule used for the estimation, on thebasis of the first state of the wheel represented by the detectedinformation obtained last by the detected-information obtaining device.

(17) A wheel-state obtaining apparatus according to any one of the abovemodes (13)-(16), wherein the detected-state estimating portion includesa provisionally estimating portion operable to obtain a provisionalestimated value of the first state of the above-indicated correspondingwheel on the basis of the second state of each of the above-indicated atleast one of the plurality of wheels detected by the second-wheel-statedetecting device, and an estimated-information obtaining portionoperable to compensate the provisional estimated value of the firststate on the basis of the first state represented by the detectedinformation extracted from the wheel-side information which has beenreceived last by the receiving device, the estimated-informationobtaining portion determining the compensated provisional estimatedvalue of the first state as the estimated information.

In the wheel-state obtaining apparatus according to the above mode (17),the first state of the wheel in question which has been provisionallyestimated by the provisionally estimating portion to obtain theprovisional estimated value is compensated on the basis of the firststate represented by the latest detected information. Informationrepresentative of the provisional estimated value of the first state maybe referred to as “provisional estimated information”.

(18) A wheel-state obtaining apparatus according to any one of the abovemodes (13)-(16), wherein the detected-state estimating portion includesa provisionally estimating portion operable to obtain a provisionalestimated value of the first state of the above-indicated correspondingwheel on the basis of the second state of each of the above-indicated atleast one of the plurality of wheels detected by the second-wheel-statedetecting device, and a final-estimated-value obtaining portion operableto compensate the provisional estimated value of the first state on thebasis of a predetermined relationship between the first staterepresented by the detected information extracted from the wheel-sideinformation received last by the receiving device, and the provisionalestimated value obtained at a moment substantially coincident with amoment at which the wheel-side information was received last by thereceiving device, the final-estimated-value obtaining portiondetermining the compensated provisional estimated value of the firststate as a final estimated value of the first state.

In the wheel-state obtaining apparatus according to the above mode (18),the provisional estimated value of the first state of the wheel inquestion is compensated to obtain the final estimated value, on thebasis of the predetermined relationship between the last detected valueof the first state and the provisional estimated value obtained atsubstantially the same moment as the last detected value of the firststate. Thus, the provisional estimated value of the first state iscompensated for a difference with respect to the last detected value, byusing a predetermined compensating coefficient. For instance, thecompensating coefficient is a ratio of the last detected value and thecorresponding provisional estimated value, or a difference between thesetwo values.

In the wheel-state obtaining apparatus, the relationship between thelasted detected value of the first state and provisional estimated valueof the first state is obtained and thus updated each time the wheel-sideinformation is received by the receiving device. However, thisarrangement is not essential. For example, the relationship may be arelationship between a plurality of detected values of the first stateand a plurality of provisional estimated values of the first state, ormay be updated each time the wheel-side information has been received apredetermined number of times. Alternatively, the relationship isobtained when the ignition switch of the vehicle is turned on, and iscontinuously used while the ignition switch is held in the on state.

(19) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(18), wherein the estimated-information obtaining deviceincludes an other-wheel-dependent estimating portion operable toestimate the first state of the above-indicated corresponding wheel onthe basis of the first state of at least one other wheel of theplurality of wheels, for obtaining the estimated informationrepresentative of the estimated first state.

(20) A wheel-state obtaining apparatus according to the above mode (19),wherein the first-wheel-state detecting device is provided for each ofat least two wheels of the plurality of wheels, and the vehicle-statedetecting device includes a second-wheel-state detecting device operableto detect a second state of each of the above-indicated at least twowheels, which second state is different from the first state, theother-wheel-dependent estimating portion obtaining the estimatedinformation of one of two wheels of the plurality of wheels, byestimating the first state of the above-indicted one of the two wheels,on the basis of the second state of the two wheels detected by thesecond-wheel-state detecting device, and the first state of the other ofthe two wheels detected by the first-wheel-state detecting device.

The first state of the wheel in question is estimated on the first stateof another wheel. Namely, the first state of one of two wheels can beestimated on the basis of the first state of the other wheel, and arelationship between the first states of the two wheels which isobtained on the basis of the second states of the two wheels.

The wheel-side devices are provided for the respective two wheelsincluding the wheel in question, so that the first states of the twowheels are detected by the first-wheel-state detecting devices of therespective two wheel-side devices. In this case, the first state of thewheel in question is estimated on the basis of the first state of theother wheel represented by the detected information, which may beobtained at a moment different from the moment at which the detectedinformation representative of the first state of the wheel in questionis obtained. Thus, the first state of the wheel in question can beeffectively estimated by utilizing the first state represented by thedetected information of the other wheel.

The estimation of the first state of the wheel in question on the basisof the first state of another wheel is based on a predeterminedrelationship between the state of the vehicle (second state of the twowheels) and the first states of the two wheels.

Where the first state is a tire air pressure of each wheel, while thesecond state (state of the vehicle) is an angular velocity of the wheel,for example, the estimation of the first state of the wheel in questionon the basis of the first state of another wheel can be made if theangular velocities of the two wheels change with the tire air pressures,and are not significantly influenced by any other factors, and if thetwo wheels are placed in substantially the same condition except for thetire air pressure. Thus, the estimation requires some conditions of thevehicle, which include, for example, at least one of a condition thatthe amounts of slipping of the two wheels are within a predeterminedrange of tolerance; a condition that the loads acting on the two wheelsare substantially equal to each other; a condition that the roadwaysurface with which the wheels are held in rolling contact aresubstantially flat; and a condition that the running speed of thevehicle is held within a predetermined range.

For example, the states of the wheel in question and another wheel areactually detected to determine whether the vehicle is placed in therequired condition or conditions for estimation of the first state ofthe wheel in question on the basis of the first state of another wheel.However, this determination may be based on the detected running stateof the vehicle. For instance, it is determined that the vehicle isplaced in the required conditions, if the vehicle is running straight ata speed within a predetermined range, on a flat roadway surface, withoutan excessively slipping tendency of the wheels.

The two wheels including the wheel in question may be limited to thefront right and left wheels, or the rear right and left wheels. Thefront right and left wheels, and the rear right and left wheels have acomparatively small difference in the load acting thereon during brakingor acceleration of the vehicle, except during turning or cornering ofthe vehicle, so that these right and left wheels usually satisfy therequired conditions indicated above.

(21) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(20), wherein the vehicle-state detecting device includes asecond-wheel-state detecting device operable to detect a second state ofeach of at least one of the plurality of wheels, the above-indicated atleast one of the plurality of wheels including another wheel differentfrom the above-indicated corresponding wheel, the second state beingdifferent from the first state, and wherein the estimated-informationobtaining device includes a relation-dependent estimated-informationobtaining portion operable to estimate the first state of heabove-indicated corresponding wheel to obtain the estimated informationrepresentative of the estimated first state of the above-indicatedcorresponding wheel, on the basis of at least the second state of theabove-indicated another wheel detected by the second-wheel-statedetecting device, and on the basis of a predetermined relationshipbetween the second states of the above-indicated corresponding wheel andthe above-indicated another wheel.

In the wheel-state obtaining apparatus according to the above mode (21),the first state of the wheel in question (above-indicated correspondingwheel) is estimated on the basis of the second state of another wheeland the predetermined relationship between the second states of thewheel in question and the above-indicated another wheel. The estimationof the first state of the wheel in question does not necessarily requiredetection of the second state of the wheel in question, where therelationship between the second states of the two wheels is known.

Where the first state is an amount of change of a load acting on each ofthe two wheels, and the second state is a braking force applied to eachwheel, while the wheel in question is a front wheel, and theabove-indicated another wheel is a rear wheel, for example, the amountof change of the front wheel is detected by the first-wheel-statedetecting device, and the braking force of the rear wheel is detected bythe second-wheel-state detecting device. In this case, the ratio of thebraking force of the rear wheel and the braking force of the front wheelis predetermined and known. On the basis of this ratio of the brakingforces of the front and rear wheels, the braking force of the frontwheel can be estimated, and a total braking force applied to the vehiclecan be estimated, so that the deceleration value of the vehicle can beestimated. Based on the thus estimated deceleration value of thevehicle, the amount of change of the load acting of the front wheel canbe estimated.

Thus, the amount of change of the load of the front wheel can beestimated on the basis of the predetermined relationship between thebraking forces of the front and rear wheels, more precisely, the knownratio of the braking forces of the front and rear wheels, without havingto detect the braking force of the front wheel.

(22) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(21), wherein the vehicle-state detecting device includes asecond-wheel-state detecting device operable to detect a quantity of asecond state of each of at least two wheels of the plurality of wheels,the above-indicated at least two wheels including the above-indicatedcorresponding wheel, the second state being different from the firststate, and wherein the estimated-information obtaining device includesan estimated-information obtaining portion operable to estimate thefirst state of the corresponding wheel to obtain the estimatedinformation representative of the estimated first state of theabove-indicated corresponding wheel, on the basis of at least arelationship between the quantity of the second state of thecorresponding wheel detected by the second-wheel-state detecting device,and an average of the quantities of the second states of theabove-indicated at least two wheels detected by the second-wheel-statedetecting device.

The first state of the wheel in question can be estimated on the basisof a relationship between the quantity of the second state of the wheelin question and the average of the quantities of the second states ofthe at least two wheels including the wheel in question. Where the firststate is whether the air pressure of the tire of the wheel in questionis normal or abnormal, and the second state is the rotating speed of thewheels, for example, it is possible to determine that the tire airpressure of the wheel in question is not normal, if the ratio of therotating speed of the wheel in question to the average of the rotatingspeeds of the at least two wheels is higher than a predeterminedthreshold.

(23) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(22), wherein the vehicle-state detecting device includes asecond-wheel-state detecting device operable to detect a second state ofthe above-indicated corresponding wheel, the second state beingdifferent from the first state, and the estimated-information obtainingdevice (includes (a) a first-estimated-information obtaining portionoperable to estimate the first state of the corresponding wheel on thebasis of the first state of at least one other wheel of the plurality ofwheels, to obtain first estimated information, and (b) asecond-estimated-information obtaining portion operable to estimate thefirst state of the above-indicated corresponding wheel on the basis ofthe second state of the above-indicated corresponding wheel, to obtainsecond estimated information, and wherein the determining device (55)includes a selecting portion operable to select one of the firstestimated information and the second estimated information, when thedetermining device determines the estimated information as thewheel-state information.

Two or more methods are available to estimate the first state of thewheel in question on the basis of a state of the vehicle. Theestimated-information obtaining device provided in the wheel-stateobtaining apparatus according to the above mode (23) includes thefirst-estimated-information obtaining portion and thesecond-estimated-information obtaining portion, and the selectingportion of the determining device selects one of the first estimatedinformation and the second estimated information which are respectivelyobtained by the first-estimated-information obtaining portion and thesecond-estimated-information obtaining portion. The selecting portionmay be arranged to select a predetermined one of the two or more methodsof estimation, or select one of the methods depending upon thesituation.

For example, the plurality of methods of estimation are sequentiallyselected according to a predetermined rule, or an appropriate one of themethods is selected depending upon the condition of the vehicle when theestimated information is obtained, such that the accuracy of estimationaccording to the selected method is the highest under the specificcondition of the vehicle at the time of estimation. Alternatively, oneof the methods of estimation is given the highest priority, so that thisone method is selected as a rule, and another of the methods is selectedwhen a predetermined condition is satisfied.

(24) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(23), wherein the determining device includes (a) avehicle-state detecting portion operable to detect a state of thevehicle, and (b) a vehicle-state-dependent determining portion operableto determine one of the detected information and the estimatedinformation as the wheel-state information, on the basis of the state ofthe vehicle detected by the vehicle-state detecting portion.

(25) A wheel-state obtaining apparatus according to the above mode (24),wherein the vehicle-state detecting portion includes avehicle-running-state detecting portion operable to detect a runningstate of the vehicle, and the vehicle-state-dependent determiningportion includes a vehicle-running-state-dependent determining portionoperable to determine one of the detected information and the estimatedinformation as the wheel-state information, on the basis of the runningstate of the vehicle detected by the vehicle-running-state detectingportion.

The determination of one of the detected information and the estimatedinformation as the wheel-state information need not be based on thecondition of reception of the wheel-side information. For example, thedetermination may be based on the detected state of the vehicle, as inthe apparatus according to the above mode (24). The state of the vehicleincludes: a state of the wheels; a running state of the vehicle; anoperating state or presence of an abnormality of at least one deviceprovided on the vehicle; and an operating state of at least one membermanually operated by the operator of the vehicle. The state of thevehicle may also include a condition of the roadway surface with whichthe wheels are held in contact. The condition of the roadway surface hasa large influence on the state of the vehicle, or determines the stateof the vehicle.

The running state of the vehicle may be represented by: running speed(level of the speed, or whether the vehicle is running at a high speed);acceleration values (acceleration values in the longitudinal and lateraldirections of the vehicle); running path (whether the vehicle is turningor cornering, or running straight); and slipping states of the wheels.These running states of the vehicle can be detected by a running-speedsensor, an acceleration sensor, a yaw rate sensor, wheel speed sensors,etc., or alternatively on the basis of the operating states of avehicle-drive system, a braking system, a steering system and any otherdevices installed on the vehicle, and the operating states of anaccelerating member (accelerator pedal), a brake operating member (abrake pedal), a steering member (steering wheel) and any other membersmanually operated by the vehicle operator.

The vehicle-state-dependent determining portion may be arranged todetermine the estimated information as the wheel-state information, whenthe detected state of the vehicle (including the state of the wheels) issuitable for the estimation of the first state of the wheel in question.For example, the detected state of the vehicle is determined to besuitable for the estimation, when a rule or algorithm for the estimationis applicable in the detected state of the vehicle, or when the accuracyof detection of the vehicle state on which the first state of the wheelin question is estimated is higher than a predetermined lower limit.Where the first state is the air pressure of the tire, and the secondstate is the rotating speed of the wheel, and where the tire airpressure is estimated on the basis of a plurality of values of therotating speed of the wheel in question, the estimated information isselected as the wheel-state information, when the rotating speed of thewheel in question changes with the tire air pressure, and is notsignificantly influenced by any other factors. For instance, it isdetermined that the accuracy of estimation of the first state on thestate of the vehicle is not sufficiently high, if the rotating speed ofthe wheel in question is influenced by the condition of the roadwaysurface or if the amount of slipping of the wheel in question isrelatively large. To this end, it is required to determine whether theaccuracy of estimation of the first state of each wheel is higher than apredetermined threshold, or determine whether the state of the vehicleas a whole permits accurate estimation of the first state of the wheelin question.

The vehicle-state-dependent determining portion of the determiningdevice in the apparatus according to the above mode (25) may be arrangedto determine, as a rule, the detected information as the wheel-stateinformation, and determine the estimated information as the wheel-stateinformation, when the detected running state of the vehicle has becomecoincident with a predetermined state. Alternatively, thevehicle-state-dependent determining portion is arranged to determine, asa rule, the estimated information as the wheel-state information, anddetermine the detected information as the wheel-state information, whenthe detected running state of the vehicle has become coincident with apredetermined state.

(26) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(25), wherein the determining device includes (a) aroadway-surface detecting portion operable to detect a condition of aroadway surface on which the vehicle is running, and (b) aroadway-condition-dependent determining portion (S154) operable todetermine one of the detected information and the estimated informationas the wheel-state information, on the basis of the condition of theroadway surface detected by the roadway-surface detecting portion.

The roadway-condition-dependent determining portion may be arranged todetermine the estimated information as the wheel-state information, whenthe flatness of the roadway surface detected by the roadway-surfacedetecting portion is higher than a predetermined value. The condition ofthe roadway surface may be detected on the basis of changes of therotating speeds of the wheels, or an output of a roadway-surfacedetector arranged to detect the condition of the roadway surface on thebasis of a state of reflection of an electromagnetic wave from theroadway surface.

(27) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(26), wherein the determining device includes a determiningportion operable to determine the estimated information as thewheel-state information, when a state of change of the estimatedinformation as obtained by the estimated-information obtaining device issmaller than a predetermined state.

When the state of change of the estimated information is smaller thanthe predetermined state, the estimated information may be continuouslyselected as the wheel-state information. When the state of change of theestimated information is larger than the predetermined state, thereliability of the estimated information is considered to be low, andcontinuous use of the estimated information is not desirable, so thatthe detected information is preferably selected as the wheel-stateinformation.

(28) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(27), wherein the determining device includes an independentlydetermining portion operable to determine one of the detectedinformation and the estimated information as the wheel-state informationrepresentative of the first state of each of the plurality of wheels,such that the detected information is selected as the wheel-stateinformation of at least one of the plurality of wheels, while theestimated information is selected as the wheel-state information of theother of the plurality of wheels.

For example, the independently determining portion is arranged to makethe determination or selection of one of the detected information andthe estimated information, for each of the wheels, or for each group ofthe wheels. Accordingly, it is possible that the detected information isselected for some of the wheels, while the estimated information isselected for the other wheel or wheels.

The independently determining portion may be arranged to select eitherthe estimated information or the detected information for each of thewheels or for each group of the wheels, depending upon the states ofchange of the first state represented by the estimated information,states of slipping of the wheels, or operating states (abnormal ornormal states) of the corresponding wheel-side devices or thesecond-wheel-state detecting device. The individual wheels or differentgroups of wheels may have different situations in connection with thestates of change of the estimated first state, states of slipping andoperating states of the wheel-side devices and second-wheel-statedetecting device, so that the selection of the detected or estimatedinformation is desirably effected for each of the wheels or each groupof the wheels, independently of each other.

(29) A wheel-state obtaining apparatus according to any one of the abovemodes (5)-(28), wherein the wheel-side device further includes atransmission control device operable to control a state of transmissionof the wheel-side information from the wheel-side-informationtransmitting device.

The transmission control device may be arranged to permit or inhibit thetransmission of the wheel-side information at a predetermined interval,or change the interval of transmission of the wheel-side information, orcommands the wheel-side-information transmitting device to transmit thewheel-side information. The transmission control device may control thewheel-side-information transmitting device on the basis of the firststate of the corresponding wheel detected by the first-wheel-statedetecting device, or on the basis of a command received from thebody-side device, as described below.

(30) A wheel-state obtaining apparatus according to the above mode (29),wherein the transmission control device includes at least one of (a) atransmission permitting/inhibiting portion operable to permit or inhibittransmission of the wheel-side information from thewheel-side-information transmitting device, on the basis of a state ofchange of the first state of the corresponding wheel detected by thefirst-wheel-state detecting device, and (b) a transmission restrictingportion operable to restrict the transmission of the wheel-sideinformation from the wheel-side-information transmitting device, whenthe change of the first state detected by the first-wheel-statedetecting device is slower than a predetermined threshold.

For instance, the transmission permitting/inhibiting portion is arrangedto permit the transmission of the wheel-side information from thewheel-side-information transmitting device when the rate of change ofthe first state of the wheel in question detected by thefirst-wheel-state detecting device is higher than a predeterminedthreshold, and inhibit the transmission when the rate of change is nothigher than the threshold.

The transmission restricting portion may be arranged to restrict thetransmission of the wheel-side information when the rate of change ofthe detected first state of the wheel in question is lower than apredetermined threshold. The restriction of the transmission includesinhibition of the transmission, prolongation of the transmissioninterval, and reduction of the wheel-side information to be transmitted.

(31) A wheel-state obtaining apparatus according to the above mode(29)-(30), wherein the wheel-side device further includes (a) awheel-side-information generating device operable o generate thewheel-side information on the basis of the first state of theabove-indicated corresponding wheel detected by the first-wheel-statedetecting device, and (b) a generating-device control device operable tocontrol the wheel-side-information generating device on the basis of astate of change of the first state detected by the first-wheel-statedetecting device.

The generating-device control device may be arranged to reduce theamount of the wheel-side information generated by thewheel-side-information generating device, when the change of the firststate is smaller than a predetermined threshold. For instance, thewheel-side-information generating device is controlled by thegenerating-device control device, so as to transmit the wheel-sideinformation which merely indicates whether the first state of thecorresponding wheel is normal or abnormal, rather than the wheel-sideinformation which represents a quantity of the first state. In thiscase, the time required for transmitting the wheel-side information canbe shortened, and the amount of electric energy required for thetransmission can be reduced.

(32) A wheel-state obtaining apparatus according to any one of the abovemodes (29-(31), wherein the body-side device further includes atransmission-state-control-information transmitting device operable totransmit to the wheel-side device transmission-state control informationindicative of a state of transmission of the wheel-side information fromthe wheel-side-information transmitting device, and the wheel-sidedevice further includes a body-side-information receiving deviceoperable to receive information from the body-side device, thetransmission control device controlling the wheel-side-informationtransmitting device according to the transmission-state controlinformation received by the body-side-information receiving device.

In the wheel-state obtaining apparatus according to the above mode (32),the state of transmission of the wheel-side information from thewheel-side device is controlled on the basis of the information receivedfrom the body-side device. In other words, the state of transmission ofthe wheel-side information from the wheel-side device is controlled bythe body-side device.

The transmission-state control information transmitted from thetransmission-state-control-information transmitting device may indicatethe transmission interval of the wheel-side information, permit orinhibit the transmission of the wheel-side information at thepredetermined transmission interval, or requires the transmission per seof the wheel-side information at a given point of time.

(33) A wheel-state obtaining apparatus according to the above mode (32),wherein the transmission-state-control-information transmitting deviceis operable to transmit to the wheel-side device at least one of (a)information which permits the transmission of the wheel-sideinformation, and (b) information which requires the transmission of thewheel-side information, when an accuracy of the estimated informationobtained by the estimated-information obtaining device is lower than apredetermined threshold.

(34) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(33), wherein the first-wheel-state detecting device includesat least one of (a) an air-pressure-state detecting device operable todetect a state of an air pressure in a tire of the corresponding wheel,(b) a temperature-state detecting device operable to detect a state of atemperature of the tire, (c) a force-state detecting device operable todetect a state of forces acting on the above-indicated wheel, and (d) arotation-state detecting device operable to detect a state of rotationof the above-indicated corresponding wheel.

(35) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(34), wherein the first-wheel-state detecting device includesan air-pressure-state detecting device operable to detect a state of anair pressure in a tire of each of at least one of the plurality ofwheels, and the vehicle-state detecting device includes a speeddetecting device operable to detect a rotating speed of each of at leastone of the plurality of wheels, the estimated-information obtainingdevice including an estimated-air-pressure-information obtaining portionoperable to estimate the air pressure of each of the above-indicated atleast one of the plurality of wheels on the basis of the rotating speeddetected by the speed detecting device, to obtain estimated-air-pressureinformation representative of the estimated air pressure.

In the wheel-state obtaining apparatus according to the above mode (35),the air pressure of the tire of the wheel in question is detected by theair-pressure-state detecting device. Thus, the present wheel-stateobtaining apparatus may be referred to as “an air-pressure obtainingapparatus”.

As described above, the air pressure of the tire is detected as thefirst state of the wheel in question. The air-pressure-state detectingdevice may be arranged to detect a value of the air pressure of thetire, or effect detection as to whether the air pressure is normal ornot. Further, the vehicle-state detecting device is the speed detectingdevice to detect the rotating speed of the wheel, which is one form of astate of rotation of the wheel.

Where the air-pressure-state detecting device is arranged to detect thevalue of the air pressure of the wheel tire, theestimated-air-pressure-information obtaining portion may be arranged toestimate the value of the tire air pressure, or to effect estimation asto whether the tire air pressure is normal or not. Where theair-pressure-state detecting device is arranged to effect detection asto whether the tire air pressure is normal or not, theestimated-air-pressure-information obtaining portion may be arranged toestimate the value of the tire air pressure, or effect estimation as towhether the tire air pressure is normal or not. These possiblecombinations of the air-pressure-state detecting device and theestimated-air-pressure-information obtaining portion are applicable tothe modes which will be described.

(36) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(35), wherein the first-wheel-state detecting device includesa temperature-state detecting device operable to detect a state of atemperature of a tire of each of at least one of the plurality ofwheels, and the vehicle-state detecting device includes arunning-time/distance detecting device operable to detect at least oneof a cumulative running time and a cumulative running distance of thevehicle, the estimated-information obtaining device including anestimated-temperature-state-information obtaining portion operable toestimate the state of the temperature of the tire of each of theabove-indicated at least one of the plurality of wheels, on the basis ofat least one of the cumulative running time and distance detected by therunning-time/distance detecting device, to obtainestimated-temperature-state information representative of the estimatedstate of the temperature.

In the wheel-state obtaining apparatus according to the above mode (36),the temperature state of the tire of the wheel in question is detectedby the temperature-state detecting device, as the first state of thewheel. The temperature-state detecting device may be arranged to detecta value of the temperature of the tire, or effect detection as towhether the tire has been overheated (whether the tire temperature ishigher than a predetermined upper limit). The tire temperature riseswith an increase in the total or cumulative running time or distance ofthe vehicle. Thus, the present wheel-state obtaining apparatus may bereferred to as “a tire-temperature-state obtaining apparatus”, or “atire-temperature obtaining apparatus”.

The temperature state of the tire may be estimated on the basis of thecumulative running time or distance of the vehicle after an ignitionswitch of the vehicle has been turned on. The temperature of the tire ishigher when the cumulative running time or distance is relatively long,than when it is relatively short. It is possible to determine that thetire has been overheated, if the cumulative running time or distance ofthe vehicle has exceeded a predetermined threshold.

The cumulative running time or distance of the vehicle may be obtainedon the basis of the running state of the vehicle. In this sense, thevehicle-state detecting device is considered to include a running-statedetecting device operable to detect the running state of the vehicle.The cumulative running time of the vehicle may be a sum of times afterthe ignition switch has been turned on and during which the runningspeed of the vehicle is higher than a predetermined value. Thecumulative running distance may be a sum of running distances after theignition switch has been turned on. The temperature of the tire ishigher when the number of repetitions of acceleration and decelerationof the vehicle is relatively large than when it is relatively small.Accordingly, the temperature state of the tire may be estimated bytaking into account the accelerating and decelerating states of thevehicle.

The vehicle-state detecting device may include a rotation-statedetecting device operable to detect a rotating state of the wheel. Onthe basis of the rotating speed of the wheel, which is one form of thestate of rotation of the wheel, the vehicle running speed and distancecan be obtained.

(37) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(36), wherein the first-wheel-state detecting device includesa temperature-state detecting device operable to detect a state of atemperature of a tire of each of at least one of the plurality ofwheels, and the vehicle-state detecting device includes (a) a loaddetecting device operable to detect a load acting on each of theabove-indicated at least one of the plurality of wheels, (b) arunning-state detecting device operable to detect a running state of thevehicle, and (c) an ambient-temperature detecting device operable todetect an ambient temperature of the vehicle, the estimated-informationobtaining device including an estimated-temperature-state-informationobtaining portion operable to estimate the state of the temperature ofthe tire of each of the above-indicated at least one of the plurality ofwheels, on the basis of the detected load acting on the above-indicatedeach wheel and the detected ambient temperature and running state of thevehicle, to obtain estimated-temperature-state informationrepresentative of the estimated state of the temperature.

The load detecting device may be arranged to directly detect a loadacting on each wheel, or estimate the load on the basis of the vehicleweight, and the vehicle attitude (which may be estimated from therunning condition of the vehicle). Alternatively, the load detectingdevice is arranged to estimate the wheel load, on the basis of arelative distance between a unsprung member and a sprung member of thewheel, for each wheel. The relative distance may be detected by afloor-level sensor arranged to detect the floor level of the vehicle.The temperature of the tire tends to be higher when the average loadacting on the wheels is relatively large than when it is relativelysmall. The tire temperature also tends to be higher when the ambienttemperature of the vehicle is relatively high than when it is relativelylow, and when the cumulative running time or distance obtained on thebasis of the running state of the vehicle is relatively long than whenit is relatively short.

The accuracy of the estimated information is low when the ambienttemperature of the vehicle has abruptly changed due to starting of thevehicle from a garage or running into a tunnel, or when a change of thewheel loads is excessively large. In such cases, it is desirable todetermine the detected information as the wheel-state information. Wherethe temperature state of the wheel is estimated on the basis of theambient temperature or the wheel load, as described above, the estimatedtemperature state may abruptly change. However, the actual temperatureof the tire will not immediately change with a change in theenvironment. Accordingly, it is possible to determine the detectedinformation as the wheel-state information when the change of theambient temperature is larger than a threshold, and/or when the changeof the wheel load is larger than a threshold.

A determination as to whether the change of the wheel load is largerthan the threshold may be effected on the estimated load value or theactually detected load value. However, the determination may be effectedon the basis of the condition of the roadway surface on which thevehicle is running. The roadway surface condition may be obtained on thebasis of the rotating speeds or acceleration values of the wheels, orstates of changes of relative distances between the unsprung and sprungmembers of the vehicle. Where the roadway surface is found to be bad, itis possible to determine that the change of the wheel loads is largerthan the threshold.

(38) A wheel-state obtaining apparatus according to any one of the abovemodes (1)-(37), wherein the first-wheel-state detecting device includesa force-detecting device operable to detect at least one force acting oneach of at least one of the plurality of wheels, and the vehicle-statedetecting device includes at least one of (a) a driving-state detectingdevice operable to detect a driving state of the vehicle, (b) abraking-state detecting device operable to detect a braking state of thevehicle, and (c) a turning-state detecting device operable to detect aturning state of the vehicle, the estimated-information obtaining deviceincluding an estimated-force-information obtaining portion operable toestimate the above-indicated at least one force acting on each of theabove-indicated at least one of the plurality of wheels on the basis ofat least one of the detected accelerating, braking and turning states ofthe vehicle, to obtain estimated-force information representative of theestimated at least one force.

In the wheel-state obtaining apparatus according to the above mode (38),at least one force acting on the wheel in question is detected, so thatthe present wheel-state obtaining apparatus may be referred to as “atire-force detecting apparatus”. The at least one force acting on thetire of the wheel in question is the first state of the wheel. Theforce-detecting device may be arranged to detect at least one of forcesacting on the wheel tire in the lateral, longitudinal and verticaldirections of the vehicle.

The driving-state detecting device may include at least one of adrive-system-state detecting device operable to detect an operatingstate of a drive system of the vehicle; apower-transmission-system-state detecting device operable to detect anoperating state of a power-transmission system of the vehicle; and anaccelerating-member-state detecting device operable to detect anoperating state of an accelerating member (e.g., accelerator pedal). Onthe basis of the driving state of the vehicle, the drive torquetransmitted to each drive wheel of the vehicle and a rotating state ofthe drive shaft can be obtained, and the forces acting on the drivewheels in the longitudinal direction of the vehicle can be estimated.

The braking-state detecting device may includes at least one of abraking-force detecting device operable to detect a braking force orbraking torque applied to each wheel; and a braking-member-statedetecting device operable to detect an operating state of a brakeoperating member (e.g., a brake pedal). Where the vehicle is providedwith a braking device of friction type arranged to force a frictionmember onto a rotor rotating with each wheel, to thereby brake thewheel, the braking-state detecting device may include a device operableto detect a braking force applied from the friction member to the rotor.Where the braking device of friction type is a hydraulically operatedbraking device having a wheel brake cylinder, the braking-statedetecting device may be arranged to detect a hydraulic pressure appliedto the wheel brake cylinder, or a hydraulic pressure equivalent to thewheel brake cylinder pressure, such as a hydraulic pressure in a mastercylinder. The braking-state detecting device can detect the brakingstate of the vehicle, on the basis of which the force acting on thewheel in the longitudinal direction of the vehicle can be estimated.

The turning-state detecting device may be arranged to detect the turningor cornering state of the vehicle, on the basis of the steering angle ofthe steering wheel of the vehicle and the running speed of the vehicle.Alternatively, the turning-state detecting device is arranged to detectthe turning state on the basis of a yaw rate of the vehicle, the lateralacceleration of the vehicle, an operating state of a front or rearsteering device, or a steering angle of the wheel in question. Theturning-state detecting device may include at least one of a steeringangle sensor; a vehicle-speed sensor; a yaw rate sensor; and alateral-acceleration sensor. The turning-state detecting device canestimate the force acting on the wheel in question in the lateraldirection.

The force acting on the wheel in the longitudinal direction can beobtained on the basis of the driving and braking states of the vehicle,while the force acting on the wheel in the lateral direction (which maybe a force acting on the wheel in a direction perpendicular to thelongitudinal direction of the vehicle, or a cornering force acting onthe wheel in a direction perpendicular to the running direction of thevehicle) can be obtained on the basis of the turning state (steeringstate) of the vehicle. The force acting on the wheel in the verticaldirection may be obtained on the basis of the vehicle weight and thevehicle attitude (which may be obtained on the basis of the vehiclerunning states such as the driving, braking and turning states). Forexample, the forces acting on the rear wheels in the vertical directionare relatively large when the vehicle is in a driving or acceleratingstate and the forces acting on the front wheels in the verticaldirection are relatively large when the vehicle is in a braking state.Further, the forces acting on the right wheels or left wheels arerelatively large in a turning state of the vehicle, depending upon thedirection in which the vehicle is turning.

On the basis of the forces acting on the wheels in the longitudinal,lateral and vertical directions, it is possible to obtain the frictioncoefficient of the roadway surface, and the corning power andself-aligning torque of the vehicle.

The determining device may be arranged to determine the detectedinformation as the wheel-state information, during a traction control oran anti-lock braking control, for example, in view of a fact that it isdifficult to estimate with high accuracy the force acting on each wheelin the longitudinal direction, on the basis of the driving and brakingstates of the vehicle, while the driving forces or braking forcesapplied to the individual wheels are controlled independently of eachother.

(39) A wheel-state obtaining apparatus comprising:

-   -   a wheel-side device provided for each of at least one of a        plurality of wheels of a vehicle and including (a) a        first-wheel-state detecting device operable to detect a first        state of the above-indicated corresponding wheel, and (b) a        wheel-side-information transmitting device operable to transmit,        in a wireless fashion, wheel-side information representative of        the first state of the above-indicated corresponding wheel        detected by the first-wheel-state detecting device; and    -   a body-side device disposed on a body of the vehicle and        including (c) a receiving device operable to receive the        wheel-side information transmitted from the wheel-side        device, (d) a detected-information obtaining device operable to        obtain received-information representative of the first state of        the above-indicated corresponding wheel, from the wheel-side        information received by the receiving device, (e) a        vehicle-state detecting device operable to detect a state of the        vehicle, (f) an estimated-information obtaining device operable        to estimate the first state of the above-indicated corresponding        wheel, on the basis of at least the state of the vehicle        detected by the vehicle-state detecting device, and obtain        estimated information representative of the estimated first        state, and (g) an obtaining-device selecting portion operable to        select one of the estimated-information obtaining device and the        detected-information obtaining device.

The received-information may be referred to as “detected information”.

The wheel-state obtaining apparatus according to the above mode (39) mayincorporate any of the technical features described above with respectto the foregoing modes (1)-(38).

(40) A wheel-state obtaining apparatus comprising:

-   -   a wheel-side device provided for each of at least one of a        plurality of wheels of a vehicle and including (a) a        first-wheel-state detecting device operable to detect a first        state of the corresponding wheel, and (b) a        wheel-side-information transmitting device operable to transmit,        in a wireless fashion, wheel-side information representative of        the first state of the above-indicated corresponding wheel        detected by the first-wheel-state detecting device; and    -   a body-side device disposed on a body of the vehicle and        including (c) a receiving device operable to receive the        wheel-side information transmitted from the wheel-side        device, (d) a detected-information obtaining device operable to        obtain detected-information representative of the first state of        the corresponding wheel, from the wheel-side information        received by the receiving device, (e) a vehicle-state detecting        device operable to detect a state of the vehicle, and (f) an        estimated-information obtaining device operable, when the        wheel-side information has not been received by the receiving        device, to estimate the first state of the above-indicated        corresponding wheel, on the basis of at least the state of the        vehicle detected by the vehicle-state detecting device, and        obtain estimated information representative of the estimated        first state.

In the wheel-state obtaining apparatus according to the above mode (40),the first state of the wheel in question is estimated on the basis ofthe detected state of the vehicle, when the wheel-side information hasnot been received by the receiving device.

The present wheel-state obtaining apparatus may incorporate any of thetechnical features described above with respect to the foregoing modes(1)-(39).

(41) A vehicle-state obtaining apparatus comprising:

-   -   a remote detecting device including a first detecting device,        and a transmitting device operable to transmit, in a wireless        fashion, first-detecting-device information including        information indicative of an output of the first detecting        device; and    -   an information processing device including (a) a        remote-information obtaining device including a receiving device        operable to receive the first-detecting-device information        transmitted in a wireless fashion from the remote detecting        device, the remote-information obtaining device being operable        to obtain remote information representative of a state of the        vehicle, on the basis of the first-detecting-device information        received by the receiving device, (b) a        wire-transmission-dependent-information obtaining device        including a second detecting device and operable to obtain        wire-transmission-dependent information representative of the        state of the vehicle, on the basis of second-detecting-device        information which has been transmitted from the second detecting        device through a signal line and which includes information        indicative of an output of the second detecting device, and (c)        an information determining device operable to determine one of        the wire-transmission-dependent information and the remote        information, as vehicle-state information representative of the        state of the vehicle.

In the vehicle-state obtaining apparatus according to the above mode(41), the first-detecting-device information including the informationindicative of the output of the first detecting device is transmitted ina wireless fashion (by radio communication) to the receiving device ofthe information processing device. When the first-detecting-deviceinformation has been received by the receiving device, the remoteinformation representative of a state of the vehicle is obtained on thebasis of the received first-detecting-device information. On the otherhand, the second-detecting-device information including the informationindicative of the output of the second detecting device is transmittedthrough the signal line to the wire-transmitted-information obtainingdevice. On the basis of the received second-detecting-deviceinformation, the wire-transmission-dependent-information obtainingdevice obtains the wire-transmission-dependent informationrepresentative of the state of the vehicle. The information determiningdevice is arranged to determine or select one of the remote informationand the wire-transmission-dependent information as the vehicle-stateinformation representative of the state of the vehicle. In the presentapparatus, the information representative of the state of the vehiclecan be obtained, even in the event of an abnormality or failure of oneof the remote-information obtaining device and thewire-transmission-dependent-information obtaining device.

The first and second detecting devices are provided to obtain theinformation on which the remote information and thewire-transmission-dependent information which represent the state of thevehicle are to be obtained. These first and second detecting devices maybe arranged to detect values or quantities indicative or representativeof the state of the vehicle, or to obtain data on which the state of thevehicle can be estimated. In other words, the first-detecting-deviceinformation received by the receiving device of the remote-informationobtaining device may be direct information which directly represents thestate of the vehicle, or original information which can be used toestimate the state of the vehicle. Where the receiving device receivesthe original information, the remote-information obtaining deviceestimates the state of the vehicle on the basis of the originalinformation, to obtain estimated information. Similarly, thesecond-detecting-device information supplied to thewire-transmission-dependent-information obtaining device through thesignal line may be direct information or original information.Accordingly, the information determining device may be arranged toselect: one of the direct information, and the estimated informationobtained on the basis of the original information (more precisely, oneof the direct remote information and the estimatedwire-transmission-dependent information, or one of the estimated remoteinformation and the direct wire-transmission-dependent information); oneof the estimated remote information and the estimatedwire-transmission-dependent information; and one of the direct remoteinformation and the direct wire-transmission-dependent information.

The remote detecting device may be disposed on a rotary member of thevehicle, such as the wheels. However, this arrangement is not essential.Where the first detecting device is disposed at a position at which itis difficult to connect the first detecting device to the informationprocessing device through a signal line, the first-detecting-deviceinformation is desirably transmitted to the information processingdevice, in a wireless fashion or by radio waves. For example, thefirst-detecting-device information is transmitted to the informationprocessing device, in a wireless fashion, where the first detectingdevice is disposed on a stationary member located close to thecorresponding wheel, or where the information processing device isprovided on a tractor vehicle while the remote detecting deviceincluding the first detecting device is provided on a towed vehicleconnected to the tractor vehicle.

The vehicle-state obtaining apparatus according to the above mode (41)may incorporate any of the technical features according to the abovemodes (1)-(39).

(42) A vehicle-state obtaining apparatus according to the above mode(41), wherein the first detecting device is operable to detect one stateof the vehicle as the above-indicated state of the vehicle, while thesecond detecting device is operable to detect another state of thevehicle which is different from the above-indicated one state, and thewire-transmission-dependent-information obtaining device includes anestimating portion operable to estimate the above-indicated one state ofthe vehicle on the basis of the above-indicated another state of thevehicle detected by the second detecting device.

The first detecting device is arranged to detect one state of thevehicle. The remote information obtained on the basis of thefirst-detecting-device information indicative of the output of the firstdetecting device may be referred to as “direct information” or “detectedinformation”. On the other hand, the second detecting device is arrangedto detect another state of the vehicle, which is different from theabove-indicated one state of the vehicle. The first state of the vehicleis estimated on the basis of the second-detecting-device informationindicative of the output of the second detecting device, and informationindicative of the estimated one state of the vehicle is obtained. Thesecond-detecting-device information obtained from the second detectingdevice may be referred to as “original information”, and the informationindicative of the estimated one state of the vehicle may be referred toas “estimated information” or “indirect information”.

Even where the first detecting device is located at a position at whichone state of the vehicle can be directly detected by the first detectingdevice, it may be difficult to connect the first detecting device to theinformation processing device through a signal line. On the other hand,the second detecting device may be located at a position at which theabove-indicated one state of the vehicle cannot be directly detected bythe second detecting device, and at which another state of the vehiclethat can be used to estimate the above-indicated one state can bedetected by the second detecting device. The second detecting devicelocated at this position can be relatively easily connected to theinformation processing device through a signal line, so that thesecond-detecting-device information can be obtained by the informationprocessing device through the signal line.

In the vehicle-state obtaining apparatus according to the above mode(42), the first-detecting-device information obtained by directlydetecting the above-indicated one state of the vehicle is supplied tothe information processing device in a wireless fashion, while theoriginal information used for estimating the one state of the vehicle issupplied through a signal line. While the first-detecting-deviceinformation transmitted in a wireless fashion or by radio communicationaccurately represents the one state of the vehicle, the estimatedinformation obtained by estimating the one state on the basis of theoriginal information (second-detecting-device information) suppliedthrough the signal line does not represent the one state of the vehicleas accurately as the first-detecting-device information transmitted byradio communication. On the other hand, the original informationsupplied through the signal line can be received by thewire-transmission-dependent-information obtaining device with a highdegree of stability, than the first-detecting-device information. Thus,the information processing device obtains the two kinds of information,namely, the first-detecting-device information (detected information)and the second-detecting-device information (original information) whichhave different degrees of accuracy and stability, and one of these twokinds of information is selected by the information determining deviceof the information processing device, depending upon the specificsituation of the vehicle.

(43) A vehicle-state obtaining apparatus according to the above mode(41) or (42), wherein the remote detecting device is provided on asprung member of the vehicle, while the information processing device isprovided on an unsprung member of the vehicle.

The sprung member is a member fixed to the axles of the front and rearwheels of the vehicle, and may be selected from among the wheels,members of a suspension system, members of a braking system, and membersof a wheel-steering system.

The unsprung member is a member supported by suspension springs, and maybe selected from among members of the vehicle body and frame, members ofa vehicle drive system, and members of a power-transmission system.

The information transmitted from the remote detecting device may bereferred to as “sprung-member information”, while the informationsupplied through the signal line from the second detecting device may bereferred to as “unsprung-member information”.

(44) A vehicle-state obtaining apparatus according to any one of theabove modes (41)-(43), wherein the remote detecting device is providedon a wheel of the vehicle.

(45) A vehicle-state obtaining apparatus according to any one of theabove modes (41-(44), wherein the information determining device isoperable to determine the wire-transmission-dependent information as thevehicle-state information, when the remote information has not beenreceived by the remote-information obtaining device.

(46) A wheel-state indicating apparatus comprising:

-   -   a wheel-state obtaining apparatus as defined in any one of the        above modes (1)-(40);    -   a judging device operable to determine whether the first state        of the above-indicated corresponding wheel is normal or not; and    -   an indicator device operable, when the judging device determines        that the first state of the above-indicted corresponding wheel        is not normal, to provide an indication that the first state is        not normal.

The indicator device includes an alarming portion which is operated upondetermination that the first state of the wheel in question, forexample, tire air pressure of the wheel, is not normal. The alarmingportion is arranged to inform the operator of the vehicle that the firststate of the vehicle is not normal. The indicator device may include anindicating portion in addition to the alarming portion. The indicatingportion is arranged to indicate the detected first state of the wheel inquestion. The indicating portion may be arranged to provide anindication only when the firs state is normal, or irrespective ofwhether the first state is normal or abnormal.

The indicator device need not be a device exclusively provided toindicate the first state of the wheel, but may be an indicator deviceprovided in any other device such as a navigation system.

The present wheel-state indicating apparatus may be adapted to indicatethe state of the vehicle obtained by a vehicle-state obtaining apparatusaccording to any one of the above modes (40)-(44).

(47) A vehicle-state controlling apparatus comprising:

-   -   a wheel-state obtaining apparatus as defined in any one of the        above modes (1)-(40);    -   an actuator portion operable to control a state of the vehicle;        and    -   an actuator control portion operable to control the actuator        portion on the basis of the first state of the corresponding        wheel obtained by the wheel-state obtaining apparatus.

The actuator portion may be a braking control actuator operable tocontrol a braking state of the vehicle, a driving control actuatoroperable to control a drive system of the vehicle, a steering controlactuator operable to control a wheel-steering system of the vehicle, ora suspension control actuator operable to control a suspension system ofthe vehicle.

The first state of the wheel in question is used as main controlinformation or auxiliary control information, when the actuator portionis controlled on the basis of the first state of the wheel. On the basisof the first state of the wheel, either a control target used forcontrolling the actuator portion may be determined, or alternatively acontrol rule or a control threshold value used for controlling theactuator portion may be changed. On the firs state of the wheel, it ispossible to estimate the friction coefficient of the roadway surface, oreffect estimation as to whether the vehicle is in a critical state, forexample. It is advantageous to control the appropriate actuator portionon the basis of the first state of the wheel.

The present vehicle-state control apparatus may include an indicatordevice.

The present vehicle-state control apparatus may be adapted to controlthe state of the vehicle on the basis of the vehicle-state obtainingapparatus according to any one of the above modes (40)-(44).

(48) A wheel-state controlling apparatus comprising:

-   -   a wheel-state obtaining apparatus as defined in any one of the        above modes (1)-(40);    -   an actuator portion operable to control the first state of the        above-indicated corresponding wheel; and    -   an actuator control portion operable to control the actuator        portion such that the first state of the above-indicated        corresponding wheel obtained by the wheel-state obtaining        apparatus is held within a predetermined range.

For example, the actuator portion includes an air source capable ofapplying a compressed air into the tire of the wheel in question, and acontrol valve operable to regulate an amount of flow of the compressedair from the air source into the tire. The actuator control portion maybe arranged to control the actuator portion such that the air pressureof the tire is held within a predetermined optimum range, or such thatthe air pressure is raised when the air pressure has been lowered belowa predetermined lower limit.

The present wheel-state control device may include an indicator device.The wheel-state control device may be adapted to control the state ofthe wheel in question on the basis of the state of the vehicle obtainedby a vehicle-state obtaining apparatus according to any one of the abovemodes (40)-(44).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically showing a wheel-state obtaining apparatusaccording to one embodiment of the present invention.

FIG. 2 is a block diagram illustrating wheel-side devices and abody-side device of the above-indicated wheel-state obtaining apparatus.

FIG. 3 is a view schematically indicating a vicinity of one of thewheel-side devices of the wheel-state obtaining apparatus.

FIG. 4 is a view air pressure values obtained by the wheel-stateobtaining apparatus.

FIG. 5 is a flow chart illustrating an air-pressure-informationobtaining program stored in the body-side device.

FIG. 6 is a flow chart illustrating an indicator-device control programstored in the body-side device.

FIG. 7 is a flow chart illustrating a detected-information obtainingprogram stored in the body-side device of a wheel-state obtainingapparatus according to another embodiment of this invention.

FIG. 8 is a flow chart illustrating an estimated-information obtainingprogram stored in the body-side device of the apparatus of FIG. 7.

FIG. 9 is a flow chart illustrating an air-pressure-informationobtaining program stored in the body-side device of a wheel-stateobtaining apparatus according to a further embodiment of the invention.

FIG. 10 is a flow chart illustrating an indicator-device control programstored in the body-side device of the apparatus of FIG. 9.

FIG. 11 is a flow chart illustrating an air-pressure-informationobtaining program stored in a memory portion of the body-side device ofa wheel-state obtaining apparatus according to a still furtherembodiment of this invention.

FIG. 12 is a flow chart illustrating an air-pressure-informationobtaining program stored in a memory portion of the body-side device ofa wheel-state obtaining apparatus according to a yet further embodimentof the invention.

FIG. 13 is a view indicating air pressure values obtained by thewheel-stating obtaining apparatus of FIG. 12.

FIG. 14 is a flow chart illustrating an air-pressure-informationobtaining program stored in a memory portion of the body-side device ofa wheel-state obtaining apparatus according to still anther embodimentof the present invention.

FIG. 15 is a block diagram schematically illustrating a wheel-stateobtaining apparatus according yet another embodiment of the invention.

FIG. 16 is a flow chart illustrating an estimated-information obtainingprogram stored in the body-side device of the apparatus of FIG. 15.

FIG. 17 is a flow chart showing a portion of the program of FIG. 16.

FIG. 18 is a flow chart showing another portion of the program of FIG.16.

FIG. 19 is a flow chart illustrating a detected-information obtainingprogram stored in the body-side device of the apparatus of FIG. 15.

FIG. 20 is a flow chart illustrating a transmission control programstored in the body-side device of the apparatus of FIG. 15.

FIG. 21 is a flow chart illustrating an estimated-information obtainingprogram stored in the body-side device of a wheel-state obtainingapparatus according to a further embodiment of this invention.

FIG. 22 is a flow chart illustrating an estimated-information obtainingprogram stored in the body-side device of the apparatus of FIG. 21.

FIG. 23 is a block diagram schematically illustrating the wheel-stateobtaining apparatus of FIG. 2, and an air-pressure adjusting apparatus,according to a still further embodiment of the invention.

FIG. 24 is a flow chart schematically illustrating the wheel-stateobtaining apparatus of FIG. 2, and a vehicle control apparatus,according to another embodiment of the invention.

FIG. 25 is a flow chart schematically illustrating a tire-temperatureobtaining apparatus provided as a wheel-state obtaining apparatusaccording to still another embodiment of the present invention.

FIG. 26 is a flow chart illustrating an estimated-information obtainingprogram stored in the body-side device of the tire-temperature obtainingapparatus of FIG. 25.

FIG. 27 is a flow chart illustrating a detected-information obtainingprogram stored in the body-side device of the apparatus of FIG. 25.

FIG. 28 is a block diagram schematically illustrating a tire-forcesobtaining apparatus provided as a wheel-state obtaining apparatusaccording to another embodiment of this invention.

FIG. 29 is a block diagram schematically illustrating a braking-torqueobtaining apparatus provided as a wheel-state obtaining apparatusaccording to yet another embodiment of the invention.

FIG. 30 is a view schematically showing a vehicle-state obtainingapparatus according to still another embodiment of this invention.

FIG. 31 is a flow chart illustrating an air-pressure-informationobtaining program which is a modification of the program illustrated inthe flow chart of FIG. 5.

BEST MODE FOR CARRYING OUT THE INVENTION

Some embodiments of a wheel-state obtaining apparatus of this inventionwill be described in detail by reference to the drawings. Thewheel-state obtaining apparatus is one form of a vehicle-state obtainingapparatus. In the illustrated embodiments, an air pressure in each wheeltire of a vehicle is detected as a state of the vehicle, and a state ofthe wheel.

An air-pressure detecting apparatus provided as a wheel-state obtainingapparatus is provided with wheel-side devices 10, 12, 14 and 16 for afront right wheel FR, a front left wheel FL, a rear right wheel RR and arear left wheel RL of a vehicle, respectively, as shown in FIGS. 1 and2. The vehicle has a body which is provided with a body-side device 18.The body-side device 18 includes four receiver antennas 20, 22, 24 and26 corresponding to the respective four wheel-side devices 10-16, and anair-pressure-information obtaining device 28 which is arranged toreceive information from the wheel-side devices 10-16 through thereceiver antennas 20-26. The wheel-side devices 10-16 have the sameconstruction, and only the wheel-side device 10 corresponding to thefront right wheel FR will be described. The description of thiswheel-side device 10 applies to the other wheel-side devices 12-16.

As shown in FIG. 3, the wheel-side device 10 for the front right wheelFR is provided on a wheel 30 of the vehicle, and includes an airpressure sensor 32 operable to detect the air pressure within a tire 31of the wheel 30, a tire-information generating device in the form of anair-pressure-information generating device 34, a transmitter antenna 36,and an electric power source in the form of a battery 38. In the presentembodiment, the state of the air pressure of the tire 31 is handled as afirst state of the wheel 30, and the air pressure sensor 32 functions asa first-wheel-state detecting device operable to detect afirst-wheel-state quantity in the form of the air pressure of the tire31. The air-pressure-information generating device 34 is arranged togenerate information indicative or representative of the air pressuredetected by the air pressure sensor 32, and the transmitter antenna 36is arranged to transmit this information, in a wireless fashion, namely,by radio communication with the body-side device 18 through the receiverantenna 20. The air-pressure-information generating device 34 is oneelement of a wheel-side-device control device 40. The wheel-side device10 is operated to transmit the information representative of thedetected air pressure (which is information relating to the wheel FR,and may be referred to as “wheel-side information”) at a predeterminedtime interval. The air pressure sensor 32, air-pressure-informationgenerating device 34 and transmitter antenna 36 are supplied with anelectric energy received from the battery 38.

Like the wheel-side device 10, the wheel-side devices 12, 14, 16transmit information representative of the air pressure values of thetires of the corresponding wheels FL, RR, RL, in the same manner asdescribed above. In principle, the four wheel-side devices 10-16 areoperated to transmit the information at respective different points oftime, but at a predetermined time interval. Namely, the moments oftransmission of the information from the wheel-side devices 10-16 aredifferent or shifted from each other by a suitable length of time, butthe transmission of the information from each wheel-side device 10-16 isrepeated at the predetermined time interval.

The receiver antennas 20-26 are disposed on respective portions of thevehicle body which are located near the corresponding wheels FR, FL, RR,RL. These receiver antennas 20-26 are connected to theair-pressure-information obtaining device 28 of the body-side device 18.The air-pressure-information obtaining device 28 is principallyconstituted by a computer, and includes a reception processing portion52 serving as a detected-information obtaining device, an estimatingportion 54 serving as an estimated-information obtaining device, awheel-information determining portion 55 serving as a wheel-statedetermining device, an indicator-device control portion 56, and a memory58 serving as a memory portion. To the air-pressure-informationobtaining device 28, there are connected wheel speed sensors 60, 62, 64,66 operable to detect rotating speeds of the respective wheels FR, FL,RR, RL. These wheel speed sensors 60-66 are attached to suitable membersof the vehicle body, so as to detect the rotating speeds of rotors whichrotate with the respective wheels. The information representative of thespeeds detected by the wheel speed sensors 60-66 is not transmitted byradio communication, but is supplied to the air-pressure-informationobtaining device 28 through signal wires 69 and through an electroniccontrol unit ECU 68 (for instance, an electronic anti-lock control unitABS ECU 68 of a braking system of the vehicle). That is, the wheel speedsensors 60-66 are electrically connected to the air-pressure-informationobtaining device 28 through the signal lines 69, as indicated in FIG. 2.

In the present embodiment, the rotating state of each wheel is a stateof the vehicle, which is a second wheel state different from theabove-described first wheel state (tire air pressure). A secondwheel-state quantity indicative of the second wheel state is detected bythe wheel speed sensors 60-66 which serves as a second-wheel-statedetecting device and a vehicle-state detecting device.

The reception processing portion 52 is arranged to extract theair-pressure information representative of the detected air pressure,from the wheel-side information received through the receiver antennas20-26, and obtain detected-air-pressure information representative ofthe tire air pressure of each wheel directly detected by thecorresponding air pressure sensor 32. In this respect, thedetected-air-pressure information may be referred to as “directlyobtained information”. The detected-air-pressure information may bereferred to as “received information” since it is received through thereceiver antennas 20-26, and may also be referred to as“radio-transmitted information” or “wireless-transmitted information”since it is transmitted by radio waves. Further, thedetected-air-pressure information is information relating to the wheelswhich are unsprung members, the detected-air-pressure information may bereferred to as “unsprung-portion information”. The detected-air-pressureinformation indicates the detected values of the air pressure of thewheel tires 31, and may be abbreviated as “detected information” whereappropriate.

The estimating portion 54 is arranged to estimate the air pressurevalues of the wheel tires, on the basis of the wheel speeds detected bythe wheel speed sensors 60-66.

There is a known relationship between the amount of change of the springconstant of the tire 31 and the amount of change of the tire airpressure. The estimating portion 54 estimates the amount of change ofthe spring constant on the basis of a plurality of sets of speed data ofthe wheel in question, more precisely, on the basis of resonancefrequency obtained by frequency analysis of the speed data sets of thewheel, or by utilizing an external-disturbance observer.

In the present embodiment, the estimating portion 54 estimates the tireair pressure on the basis of a plurality of sets of speed data of thewheel in question, and according to the known relationship describedabove. The estimating portion 54 compensates the thus estimated airpressure on the basis of the detected air pressure value of the wheeltire in question, and obtains estimated-air-pressure informationrepresentative of the estimated air pressure thus compensated. The airpressure value estimated on the basis of the speed data sets of thewheel and according to a predetermined rule such as the knownrelationship described above will be hereinafter referred to as “aprovisional estimated value” of the air pressure, while the provisionalestimated value compensated on the basis of the detected value obtainedon the basis of the output of the pressure sensor 32 will be referred toas “a final estimated value”. In a broad sense, the provisionalestimated value and the final estimated value are both estimated values,and the information representative of the provisional estimated valueand the information representative of the final estimated value are bothestimated-air-pressure information. In a narrow sense, however, only thefinal estimated value is considered to be the estimated value, and onlythe information representative of this final estimated value isconsidered to be the estimated-air-pressure information. Theestimated-air-pressure information (which may be abbreviated as“estimated information”, where appropriate), which is not directlydetected, may be referred to as “indirectly obtained information”. Sincethe wheel speed values are represented by output signals of the wheelspeed sensors 60-66 which are fed to the air-pressure informationobtaining device 28 through the signal lines 69, the estimatedinformation may be referred to as “wire-transmission-dependentinformation (cable-transmission-dependent information)”.

The term “air-pressure information” used hereinafter means informationrepresentative of an air pressure of the tire 31, the magnitude of whichis referred to as “an air pressure value”.

The wheel-information determining portion 55 is arranged to determineeither one of the detected information and the estimated information asthe air-pressure information. Described more specifically, thewheel-information determining portion 55 determines the detectedinformation as the air-pressure information where the wheel-sideinformation has been normally received through the receiver antenna20-26. If the wheel-side information has not be normally receivedthrough the receiver antenna 20-26 at a predetermined timing ofreception, the wheel-information determining portion 55 determines theestimated information as the air-pressure information at a predeterminedtiming of calculation during a period of reception of the wheel-sideinformation, as described below in greater detail.

The indicator-device control portion 56 is arranged to determine whetherthe air pressure value represented by the air-pressure informationobtained by one of the reception processing portion 52 and theestimating portion 54 is lower than a predetermined threshold value, andcontrols the indicator device 70 on the basis of a result of thedetermination. The indicator-device control portion 56 effects thedetermination on the basis of the detected air pressure valuerepresented by the detected information or the estimated air pressurevalue represented by the estimated information. The indicator-devicecontrol portion 56 may be considered to function as a judging portionoperable to determine whether the detected or estimated air pressurevalue is normal or not.

The indicator device 70 includes an indicating portion 72 arranged toindicate the air pressure value, and an alarming portion 74 arranged togenerate a warning or alarming signal. The indicating portion 72indicates the information received from the indicator-device controlportion 56, and the alarming portion 74 is operated when the airpressure value represented by the received information is lower than thethreshold value.

As described above, the receiver antennas 20-26 receive the wheel-sideinformation at the predetermined time interval (reception time interval)to obtain the detected air-pressure information, while the wheel-sidedevices 10-16 transmit the wheel-side information at the predeterminedtime interval (transmission time interval).

Where the reception processing portion 52 cannot obtain thedetected-air-pressure information for a certain one of the wheels, theindicator-control portion 56 determines the estimated-air-pressureinformation as the air-pressure information. For instance, theindicator-control portion 56 determines the estimated-air-pressureinformation as the air-pressure information, if the correspondingreceiver antenna 20, 22, 24, 26 has not received the wheel-sideinformation during the present period of reception following the lastmoment of reception of the wheel-side information according to thepredetermined transmission or reception interval, due to an abnormalityof the receiver antenna 20-26 or a noise received by the receiverantenna, or if the corresponding wheel-side device 10, 12, 14, 16 hasnot transmitted the wheel-side information during the present period oftransmission following the last moment of transmission of the wheel-sideinformation. In this respect, the reception interval (period ofreception) and the transmission interval (period of transmission) areconsidered to be the same as long as the receiver antennas 20-22 arenormal and are free from a noise.

While the provisional estimated value and the detected value of the airpressure which have been described are usually coincident with eachother, there may be a difference between these two values, as indicatedin FIG. 4. This difference may be corrected (zeroed or reduced)according to a ratio of the provisional estimated value and the detectedvalue to each other or the difference per se. Namely, the provisionalestimated value is compensated into the final estimated value, on thebasis of the above-indicated ratio or difference used as a compensationcoefficient or amount.

In view of the above, the present embodiment is arranged such that theratio of the provisional estimated value and the detected valuerepresented by the detected-air-pressure information is obtained as thecompensation coefficient when the information is received. The presentembodiment is further arranged to update this ratio each time thedetected information is received, that is, to update the ratio on thebasis of the last detected information, so that the provisionalestimated value is compensated into the final estimated value, on thebasis of the ratio determined on the basis of the last detectedinformation. Thus, the present embodiment is arranged such that the airpressure value estimated on the basis of the detected wheel speed andaccording to the predetermined rule is compensated into the finalestimated value, on the basis of the last detected air pressure value.In other words, the compensating coefficient is updated on the basis ofthe last detected air pressure value, and the provisional estimatedvalue of the air pressure is compensated into the final estimated valueon the basis of the thus updated compensation coefficient. Accordingly,the final estimated value thus obtained is made close to the actual airpressure value. It can also be said that the rule of estimation of theair pressure value on the basis of the detected wheel speed is changedor determined on the basis of the compensation coefficient or lastdetected value.

Although the present embodiment is arranged to update the compensationcoefficient each time the detected air-pressure information is obtained,this arrangement is not essential. For example, the compensationcoefficient may be updated each time the detected-air-pressureinformation has been received a predetermined number of times.Alternatively, the compensation coefficient may be made equal to anaverage of a plurality of ratio values of the detected value and theprovisional estimated value.

The air-pressure-information obtaining device 28 is arranged to executean air-pressure-information obtaining program illustrated in the flowchart of FIG. 5, with a predetermined cycle time, for each of the wheelsFR, FL, RR, RL independently of each other, since the reception timingsof the wheel-side information of the four wheels are different from eachother.

The air-pressure-information obtaining program is initiated with step S1to determine whether the present point of time is the predeterminedtiming of calculation of the provisional estimated value of the airpressure, that is, one of predetermined moments of calculation of theprovisional estimated value.

In the present invention, the calculation of the provisional estimatedvalue is effected at the predetermined moments of calculationrepresented by t₁, t₁+ΔT₂, t₁+2ΔT₂, . . . t₁+k≢T₂, as indicated in FIG.4. The calculation period or interval is ΔT₂, so that an affirmativedecision (YES) is obtained in step S1 each time the calculation periodΔT₂ has passed. In FIG. 4, “t₁” and “t₂” indicate the timing ofreception of the wheel-side information, while “ΔT₁” indicates thereception period or interval, so that an affirmative decision (YES) isobtained in step S5 (which will be described) each time the receptionperiod ΔT₁ has passed.

The calculation period ΔT₂ is a fraction of the reception interval orperiod ΔT₁, more precisely, equal to ΔT₁/n, where “n” is an integer.Therefore, each moment of reception of the wheel-side information is themoment of calculation of the provisional estimated value, so that thereexist a plurality of moments (n−1) of calculation during the receptioninterval ΔT₁. The calculation interval ΔT₂ is determined to be longenough to permit a sufficiently large number of sets of data of thewheel speed to be received to estimate the air pressure. The wheel speeddata set is received through the electronic anti-lock control unit ABSECU 68 at a predetermined time interval.

If a negative decision (NO) is obtained in step S1, the control flowgoes to steps S2 and S3 to read the wheel speed and store the wheelspeed in a memory portion in the form of the memory 58.

If an affirmative decision (YES) is obtained in step S1, the controlflow goes to step S4 to obtain the provisional estimated value of theair pressure on the basis of a plurality of wheel speed values which arestored in the memory 58 and which include the wheel speed value storedlast in step S1.

Then, the control flow goes to step S5 to determine whether the presentpoint of time is one of the moments of reception of the wheel-speedinformation. If an affirmative decision (YES) is obtained in step S5,the control flow goes to steps S6 and S7 to determine whether thewheel-side information has been received through the correspondingreceiver antenna 20, 22, 24, 26 within the preset time. If anaffirmative decision (YES) is obtained in step S6, the control flow goesto steps S8 and S9 to process the received wheel-side information, forthereby obtaining the detected-air-pressure information indicative orrepresentative of the detected air pressure value.

Step S9 is followed by step S10 to calculate the compensationcoefficient γ, namely, a ratio γ of the provisional estimated valueP_(INDIRECT)(t₁) and the detected value P_(DIRECT)(t₁) which have beenobtained at substantially the same moment as the moment at which thedetected-air-pressure information was obtained. That is, the ratio γ isP_(DIRECT)(t₁)/P_(INDIRECT)(t₁). As described below, a difference “s”between the provisional estimated value P_(INDIRECT)(t₁) and thedetected value P_(DIRECT)(t₁) may be used as the compensationcoefficient γ. Namely, the difference “s” is equal to P_(DIRECT)(t₁)minus P_(INDIRECT)(t₁).

The control flow then goes to step S12 to determine the detected airpressure as the tire air pressure value, and to step S13 to clear thememory 58 for erasing the wheel speed data stored therein.

If the wheel-side information has not been received by the receiverantenna until the preset time has elapsed after the predetermined timingof reception, an affirmative decision (YES) is obtained in step S7, andthe control flow goes to step S11 to obtain the final estimated valueP(t₁+kΔT₂) according to the following equation (1) or (2), on the basisof the compensation coefficient γ and the provisional estimated valueP_(INDIRECT)(t₁):P(t ₁ +kΔT ₂)=γ×P _(INDIRECT)(t ₁ +kΔT ₂)  (1)P(t ₁ +kΔT ₂)=s+PINDIRECT(t ₁ +kΔT ₂)  (2)

While the affirmative decision (YES) is obtained in step S1 and anegative decision (NO) is obtained in step S5, the step S11 is alsoimplemented.

Step S11 is followed by step S12 in which the final estimated value isdetermined as the tire air pressure. In the present embodiment, thefinal estimated value is obtained if the present point of time is notone of the moments of reception of the wheel-side information, or if thewheel-side information has not been received within the present time (orif the information representative of the first-wheel-state quantity ortire air pressure has not been received due to absence or defect of thewheel-side information or due to abnormality of the receiver antenna20-26, for example).

Where the wheel-side devices 10-16 are arranged to transmit theair-pressure information at different transmission intervals, theshortest transmission interval is used as the reception interval orperiod ΔT₁, and the calculation period or interval ΔT₂ is determined toa fraction of the shortest transmission interval.

On the basis of the air pressure value thus obtained, the indicatordevice 70 is controlled according to an indicator-device control programillustrated in the flow chart of FIG. 6. That is, when the air pressurevalue is lower than a predetermined threshold value P0, an affirmativedecision (YES) is obtained in step S17 of the flow chart of FIG. 6, andthe control flow goes to steps S18 and S19 to activate the alarmingportion 74 of the indicator device 70 and active the indicating portion72 to indicate the obtained air pressure value. When the air pressurevalue is not lower than the threshold value P0, a negative decision (NO)is obtained in step S17, and the control flow goes to step S19 whileskipping step S18, so that the detected air pressure is indicated on theindicating portion 72, without activation of the alarming portion 74.

As described above, the present embodiment is arranged to estimate thetire air pressure of a wheel on the basis of the wheel speed, if the airpressure cannot be detected on the basis of the output of the pressuresensor 32. Further, the air pressure is also estimated while thenegative decision (NO) is obtained in step S5. Thus, thedetected-air-pressure information or the estimated-air-pressureinformation is determined as the air-pressure information, for each ofthe wheels, so that the transmission period or interval ΔT₁ of thewheel-side devices 10-16 can be made relatively long, whereby the rateof reduction of the electric energy amount stored in the battery 38 canbe lowered, resulting in a prolonged service life of the battery 38.Further, the present embodiment makes it possible to obtain the airpressure value of each wheel even in the event of a failure orabnormality of the wheel-side devices 10-16, receiver antennas 20-26, oreven in the event of failure to obtain the detected-air-pressureinformation due to a noise received by the receiver antenna 20-26. Theair pressure value can be obtained at least at the predeterminedreception interval ΔT₂, which is determined by the predeterminedtransmission interval ΔT₁.

Further, the provisional estimated value of the air pressure iscompensated on the basis of the last detected air pressure value, toobtain the final estimated value which is sufficiently close to theactual air pressure value. The present embodiment is arranged such thatif the detected air pressure value is not obtained in the present cycle,the provisional estimated value obtained in the present cycle iscompensated into the final estimated value, on the basis of the lastdetected air pressure value obtained at the last moment of reception ofthe wheel-side information by the receiver antenna 20-26, so that thefinal estimated value is obtained on the basis of the last detected airpressure value.

It will be understood from the foregoing description of the presentembodiment that a portion of the air-pressure-information obtainingdevice 28 assigned to implement steps S8 and S9 of the flow chart ofFIG. 5 constitutes a detected-air-pressure-information obtaining devicein the form of the reception processing portion 52, while a portion ofthe obtaining device 28 assigned to implement steps S2-S4 and S11constitutes an estimated-air-pressure-information obtaining device inthe form of the estimating portion 54. It will also be understood thatthe estimated-air-pressure-information obtaining device also functionsas a reception-failure estimated-air-pressure-information obtainingportion operable to obtain the estimated air-pressure information whenthe detected-air-pressure information cannot be received, and alsofunctions as a detected-state estimating portion operable to compensatethe provisional estimate value on the basis of the last detected airpressure value, to obtain the final estimated value. It will further beunderstood that a portion of the air-pressure-information obtainingdevice 28 assigned to implement steps S5-S7 constitutes thewheel-information determining portion 55. Since this determining portion55 determines one of the detected-air-pressure-information obtainingdevice and the estimated-air-pressure-information obtaining device,depending upon the determinations in steps S5-S7, the determiningportion 55 may be referred to as “an information-obtaining-devicedetermining device”. The receiver antennas 20-26 may be considered toconstitute a part of the reception processing portion 52.

In the embodiment of FIG. 5, the received wheel-side information isprocessed in step S8, and the detected-air-pressure information isobtained in step S9, on the basis of the processed wheel-sideinformation. However, the air-pressure-information obtaining program ofFIG. 5 may be replaced by an air-pressure-information obtaining programillustrated in the flow chart of FIG. 31. In the modified arrangement ofFIG. 31, the step S8 in which the received wheel-side information isprocessed is followed by step S8 a to determine whether the air pressurevalue represented by the processed air-pressure information is normal.If the air pressure value is determined to be abnormal, a negativedecision (NO) is obtained in step S8 a, and the control flow goes tostep S11 to obtain the final estimated value. For instance, the negativedecision is obtained in step S8 a, if the air pressure value per se isabnormal due to an abnormality of the air pressure sensor 32. In thiscase, the detected-air-pressure information is not obtained in step S9,but the final estimated value is obtained in step S11, in the samemanner as described above.

The detected-air-pressure-information obtaining device (receptionprocessing portion 52) and the estimated-air-pressure-informationobtaining device (estimating portion 54) may be constituted by a singlecomputer or respective separate computers.

Similarly, the indicator-device control portion 56 may be constituted bya computer which constitutes the reception processing portion 52 and/orthe estimating portion 54, or by a computer different from the computeror computers which constitute(s) the portion 52 and/or the portion 54.Where those portions 52, 54, 56 are constituted by respective separatecomputers, mutual data communication is effected among the separatecomputers, such that when a data-request signal is transmitted from oneof the computers to the other computer or computers, this one computerreceives necessary data from the other computer or computers, or suchthat predetermined kinds of updated or latest data are stored in aninput-output interface of each computer, so that one of the computerscan read in necessary data from the input-output interface of the othercomputer or computers. Thus, the mutual data communication is effectedbetween one of the computers and the other computer or computers.

Referring next to FIGS. 7 and 8, there will be describeddetected-information obtaining programs to obtain thedetected-air-pressure information and anestimated-air-pressure-information obtaining program to obtain theestimated-air-pressure information, according to another embodiment ofthe present invention. The detected-information obtaining program ofFIG. 7 is executed by the reception processing portion 52, while theestimated-information obtaining program of FIG. 8 is executed by theestimating portion 54. In the program of FIG. 7, step S21 is implementedto supply the estimating portion 54 with information permitting the useor determination of the estimated-air-pressure information as theair-pressure information, if the reception portion 52 has not receivedthe wheel-side information, that is, if the negative decision isobtained in step S5, or if the wheel-side information has not beenreceived within the present time. If the affirmative decision isobtained in step S6 within the preset time, the control flow goes tosteps S8 and S9 to obtain the detected-air-pressure information, asdescribed above, and then goes to steps S22 in which the compensationcoefficient γ is obtained on the basis of the latest one of theprovisional estimated values. Step S22 is followed by step S23 to supplythe estimating portion 54 with the obtained compensation coefficient γ.Then, the control flow goes to step S24 to supply the indicator-devicecontrol portion 56 with the detected-air-pressure information P_(DIRECT)as the air-pressure information P, and to step S25 to supply theestimating portion 54 with information inhibiting the use ordetermination of the estimated-air-pressure information P_(INDIRECT) asthe air-pressure information.

If the estimating portion 54 has been supplied with the informationpermitting the determination of the estimated-air-pressure informationas the air-pressure information, an affirmative decision (YES) isobtained in step S27 of the program of FIG. 8, and the control flow goesto step S28 to calculate the final estimated value on the basis of thecompensation coefficient γ received from the reception processingportion 52. Step S28 is followed by step S29 in which theindicator-device control portion 56 is supplied with theestimated-air-pressure information as the air-pressure information. Ifthe estimating portion 54 has not been supplied with the informationpermitting the determination of the estimated-air-pressure informationas the air-pressure information, a negative decision (NO) is obtained instep S27, and the final estimated value is not calculated.

It is noted that if the provisional estimated value is calculated instep S4 as described above, the control flow goes to step S26 in whichthe reception processing portion 52 is supplied with the calculatedestimated value.

In the embodiment of FIGS. 7 and 8 described above, the informationpermitting or inhibiting the determination of the estimated-air-pressureinformation as the air-pressure information is supplied from thereception processing portion 52 to the estimating portion 54, so thatone of the detected-air-pressure information and theestimated-air-pressure information is determined as the air-pressureinformation. In the present embodiment, a portion of the receptionprocessing portion 52 assigned to implement steps S6 and S7 may beconsidered to constitute the wheel-information determining portion 55.In this case, the wheel-information determining portion 55 may beconsidered to be included in the reception processing portion 52. In thefollowing embodiments, too, the estimated-air-pressure information andthe detected-air-pressure information may be obtained by a single commoncomputer or by respective separate computers.

The detected-air-pressure-information obtaining device may beconstituted by a hardware circuit.

It is not essential to obtain the final estimated value of the airpressure by compensating the provisional estimated value. Namely, theprovisional estimated value is obtained at a predetermined timing ofcalculation, and is determined as the air-pressure value. In thisinstance, steps S10 and S11 of the program of FIG. 5 are not necessary,and one of the provisional estimated value and the directly detectedvalue is determined as the air pressure value. Similarly, steps S22 andS23 of the program of FIG. 7, and steps S26 and S28 of the program ofFIG. 8 are not necessary.

It is not essential that the wheel-state obtaining apparatus accordingto the present invention is arranged to estimate the tire air pressureof each wheel of the vehicle. For instance, the wheel-state obtainingapparatus may be arranged to determine by estimation whether the airpressure of each wheel is normal or not. To the vehicle operator,information as to whether the air pressure of each wheel is normal ornot is helpful. For example, the wheel-state obtaining apparatus isarranged to determine that the air pressure of each wheel is lower thana predetermined value (and is abnormal), if a ratio α of the speed ofthat wheel to an average speed of the four wheels is higher than apredetermined threshold value α0. The ratio α is calculated according tothe following equation (3), and the air pressure of each wheel isdetermined to be abnormal, if the following inequality (4) is satisfied.α=Vwi/(ΣVwi/4)  (3)α>α0  (4)

When the tire air pressure of each wheel is relatively low, theeffective radius of the wheel (tired wheel) is smaller than when thetire air pressure is relatively high, the rotating speed (angularvelocity) of the wheel is higher when the air pressure is relatively lowthan when it is relatively high. The determination as to whether thetire air pressure of each wheel is normal or not is preferably effectedwhile the vehicle is running straight at an almost constant speed.

The flow chart of FIG. 9 illustrates an air-pressure-informationobtaining program according to a further embodiment of this invention,which is formulated to determine whether the tire air pressure of eachwheel is normal or not. In this program, an affirmative decision(YES) isobtained in step S6 when the wheel-side information has been receivedthrough the corresponding receiver antenna 20, 22, 24, 26. In this case,the control flow goes to steps S8 and S9 to process the receivedwheel-side information and obtain the detected-air-pressure information.Step S9 is followed by step S31 to determine whether the air pressurerepresented by the detected-air-pressure information is higher than athreshold value P0. If the air pressure is equal to or lower than thethreshold value P0, the control flow goes to step S32 to determine thatthe air pressure is abnormal. If the air pressure is higher than thethreshold value P0, the control flow goes to step S33 to determine thatthe air pressure is normal.

If the negative decision (NO) is obtained in step S5, or if thewheel-side information has not been received by the antenna 20, 22, 24,26 within the preset time (if the affirmative decision (YES) is obtainedin step S7), the control flow goes to step S34 to read the speeds of thefour wheels FR, FL, RR, RL, and then to step S35 to calculate the ratioα of the speed of the wheel in question to the average speed of all ofthe four wheels. Step S35 is followed by step S36 to determine whetherthe calculated ratio α is higher than the predetermined threshold valueα0. If the ratio α is higher than the threshold value α0, the controlflow goes to step S32 to determine that the air pressure of the wheel inquestion is abnormal. If the ratio α is not higher than the thresholdvalue α0, the control flow goes to step S33 to determine that the airpressure of the wheel in question is normal.

In the present embodiment, the indicator device 70 is controlledaccording to an indicator-device control program illustrated in the flowchart of FIG. 10. If the air pressure has been determined to beabnormal, a negative decision (NO) is obtained in step S41, and thecontrol flow goes to step S42 to active the alarming portion 74. If theair pressure has been determined to be normal, an affirmative decision(YES) is obtained in step S41, and the alarming portion 74 is notactivated.

Where the detected-air-pressure information is obtained, the detectedair pressure value may be indicated on the indicating portion 72. Forexample, the indicating portion 72 keeps indicating the last detectedair pressure value until the detected-air-pressure information isobtained at the next timing of reception of the wheel-side information.Where the detected air pressure value is determined to be abnormal, thealarming portion 74 is activated to generate a warning or alarmingsignal.

It is not essential to estimate the air pressure at the predeterminedinterval of reception of the wheel-side information. For instance, theair pressure is estimated only when the wheel-side information has notbeen received due to an abnormality of the corresponding receiverantenna 20, 22, 24, 26 or a noise received by the receiver antenna. Inthis instance, the estimated-air-pressure information rather than thedetected-air-pressure information is determined as the air-pressureinformation. In the first and second embodiments of FIGS. 5-8, forexample, the provisional estimated value is used as the air pressurevalue.

The flow chart of FIG. 11 illustrates an air-pressure-informationobtaining program which is executed with a predetermined cycle time andwhich is formulated to estimate the air pressure only when thewheel-side information has not been received within the preset time.When the present point of time is not the predetermined timing ofreception of the wheel-side information, the negative decision (NO) isobtained in step S5, and the control flow goes to steps S61 and S62 toread the wheel speed and store it in the memory 58. At the predeterminedtiming of reception of the wheel-side information, the control flow goesto steps S6 and S7 to determine whether the wheel-side information hasbeen received within the preset time. If the wheel-side information hasbeen received, the control flow goes to steps S8 and S9 to process thereceived wheel-side information and obtain the detected-air-pressureinformation. Step S9 is followed by step S12 to determine thedetected-air-pressure information as the air-pressure information.

If the wheel-side information has not been received within the presenttime after the predetermined timing of reception of the wheel-sideinformation, the control flow goes to step S63 to estimate the airpressure of the wheel in question on the basis of a plurality of wheelspeed values stored in the memory 58, for thereby obtaining theestimated-air-pressure information. Step S63 is followed by step S12 inwhich the estimated-air-pressure information is determined as theair-pressure information. Thus, the air-pressure information isnecessarily obtained at the predetermined timing of reception of thewheel-side information, even if the wheel-side information has not beenobtained, that is, even if the affirmative decision (YES) is obtained instep S7.

Where the wheel-side information has not been received by the receiverantenna 20-26 within the preset time, due to an abnormality of thewheel-side device 10-16, step S12 to determine theestimated-air-pressure information as the air-pressure information isrepeatedly implemented, with the affirmative decision (YES) beingobtained in step S7 as long as the abnormality is eliminated.

In the present embodiment, a portion of the air-pressure-informationobtaining device 28 assigned to implement step S63 of the program ofFIG. 11 constitutes the reception-failureestimated-air-pressure-information obtaining portion described above. Aportion of the program assigned to implement steps S5-S7 and S63 may beconsidered to constitute the reception-failureestimated-air-pressure-information obtaining portion.

The air pressure of each wheel may be estimated on the basis of thedetected air pressure value of another wheel.

Between two wheels, there is a relationship in which a ratio β of therotating speeds (angular velocities) ω of the two wheels is equal to areciprocal of a ratio of the air pressure values P of the two wheels.This relationship is represented by the following equation (5):β=ωj/ωi=P′i/P*j  (5)

In the above equation (5), “i” and “j” represent the wheels FR, FL, RRand RL, and “P′” represents the estimated value while “T*” representsthe detected value. The effective radius of a wheel (tired wheel) whenthe tire air pressure of the wheel is relative low is smaller than whenthe tire air pressure is relatively high, so that the rotating speed ofthe wheel is higher when the air pressure is relatively low than when itis relatively high. Accordingly, the air pressure P′i of one of the twowheels i and j can be estimated on the basis of the ratio β of thespeeds ω of the two wheels and the detected air pressure P*j of theother wheel, according to the following equation (6)P′i=β·P*j  (6)

In this case, an air-pressure-information obtaining program illustratedin the flow chart of FIG. 12 is executed with a predetermined cycletime. According to this air-pressure-information obtaining program, theair pressure P′i of one wheel i is estimated on the basis of thedetected air pressure value P*j of another wheel j and the ratio β ofthe detected speeds ω of the two wheels i and j. In the specific exampleof FIG. 12, the air pressure value P′_(FR) of the front right wheel FRis estimated on the basis of the detected air pressure value P*_(FL),P*_(RR) or P*_(RL) of the other wheels FL, RR, RL, as described below Idetail.

The program is executed to determine in steps S71-S74 whether thewheel-side information has been received by the antennas 20-26corresponding to the four wheels FR, FL, RR and RL. If the wheel-sideinformation has been received by the receiver antenna 20 correspondingto the front right wheel FR, steps S75 and S76 are implemented to obtainthe detected-air-pressure information, and step S95 is implemented todetermine the obtained detected-air-pressure information as theair-pressure information.

If the wheel-side information has not been received by the receiverantenna 20 for the front right wheel FR, and if the wheel-sideinformation has been received by the receiver antenna 22 for the frontleft wheel FL, an affirmative decision (YES) is obtained in step S72,and the control flow goes to steps S77 and S78 to process the receivedwheel-side information and obtain the detected-air-pressure information,and to steps S79 and S80 to obtain the ratio β=ωFL/ωFR of the speeds ofthe two front wheels FR, FL. Step S80 is followed by step S81 tocalculate the estimated air pressure value P′_(FR) of the front rightwheel FR on the basis of the ratio β and the detected air pressureP*_(FL) of the front left wheel FL, and according to the above-indicatedequation (6). Then, the control flow goes to step S95 to determine theestimated air pressure value P′_(FR) as the air pressure of the frontright wheel FR.

If the wheel-side information has not been received by the antennas 20,22 for the front right and left wheels FR, FL, and if the wheel-sideinformation has been received by the receiver antenna 24 for the rearright wheel RR, steps S82-S86 similar to steps S77-S81 are implementedto calculate the estimated air pressure value P′_(FR) of the front rightwheel FR on the basis of the detected air pressure value P*_(RR) of therear right wheel RR and the ratio β of the speeds of the wheels FR andRR.

If the wheel-side information has not been received by the receiverantennas 20, 22, 24 for the wheels FR, FL and RR, and if the wheel-sideinformation has been received by the receiver antenna 26, steps S88-S92similar to steps S77-S81 are implemented to calculate the estimated airpressure value P′_(FR) of the front right wheel FR on the basis of thedetected air pressure value P*_(RL) of the rear left wheel RL and theratio β of the speeds of the wheels FR and RL.

The air pressure values obtained in the embodiment of FIG. 12 areindicated in FIG. 13.

In the present embodiment, the wheel-side information is transmittedfrom the four wheel-side devices 10-16 at substantially the sametransmission interval such that the moments of transmission of thewheel-side information from the wheel-side devices 10-16 are differentor shifted from each other by a suitable length time, as previouslydescribed. Accordingly, during the interval of transmission from onewheel-side device, the wheel-side information (air-pressure information)is received by the receiver antennas corresponding to the otherwheel-side devices, at respective different moments, so that the airpressure P′_(FR) of the front right wheel FR, for example, can beestimated on the basis of the air pressure value P*_(FL), P*_(RR) orP*_(RL) of the other wheel which is detected during the transmissioninterval t1-t2 of the wheel-side device 10 corresponding to the frontright wheel FR, as indicated in FIG. 13, by way of example.

In the same manner as described above with respect to the front rightwheel FR, the air pressure values P′_(FL), P′_(RR) and P′_(RL) of thewheels FL, RR, RL can be estimated on the basis of the detected airpressure value P* of the other wheel and the ratio of the two wheels inquestion. In the present embodiment, a portion of theair-pressure-information obtaining apparatus 28 assigned to implementsteps S77-S81, S82-S86 and S88-S92 constitutes an other-wheel-dependentestimated-air-pressure-information obtaining device operable to obtainthe estimated air pressure value of one of the wheels on the basis ofthe detected air pressure value of another of the wheels.

In the embodiment of FIG. 5, the air pressure of one of the wheels whoseinformation has not been received is estimated on the basis of thedetected air pressure value of another wheel. However, the air pressuresof two or more of the four wheels may be estimated on the basis of thedetected air pressure value of a predetermined reference wheel which isselected from the four wheels. An example of an air-pressure-informationobtaining program according to this modification is illustrated in theflow chart of FIG. 14. This program is initiated with step S101 todetermine whether the wheel-side information of the predeterminedreference wheel, for example, of the front right wheel FR, has beenreceived by the corresponding receiver antenna (e.g., receiver antenna20). If an affirmative decision (YES) is obtained in step S101, thecontrol flow goes to steps S102 and S103 to process the receivedwheel-side information and obtain the detected air pressure valueP*_(FR). Then, the control flow goes to step S104 to read the rotatingspeeds of the four wheels, and to steps S105-S107 to calculate theratios of the speed of the reference wheel FR to the speeds of the otherwheels FL, RR and RL, and obtain the estimated air pressure valuesP′_(FL), P′_(RR) and P′_(RL) of the wheels FL, RR and RL, on the basisof the calculated ratio and the detected air pressure value P*_(FR) ofthe reference wheel FR.

For the reference wheel FR, the detected air pressure value P*FR is usedas the tire air pressure. For the other wheels FL, RR, RL, the estimatedair pressure values P′_(FL), P′_(RR) and P′_(RL) are used as their tirepressure values. In this case, the provision of the wheel-side devices12, 14, 16 for the wheels FL, RR, RL is not essential, and the cost ofmanufacture of the wheel-state obtaining apparatus can be reduced.

Where the air pressure of one wheel is estimated on the basis of thedetected air pressure of another wheel, this estimation may be inhibitedduring a run of the vehicle on a bad roadway. While the vehicle isrunning on a bad roadway, the two wheels do not usually have therelationship represented by the above-indicated equation (5) between theratio of the speeds and the ratio of the air pressures. For example, arun of the vehicle on a bad roadway is detected when the wheel speedsare changing at a relatively high rate and when the frequency of changeof the wheel speeds is relatively high. This running condition of thevehicle may be detected by using a vertical acceleration sensor disposedon a sprung member of the vehicle. When the high-frequency component ofthe output of the vertical acceleration sensor is larger than athreshold value, it is considered that the vehicle is running on a badroadway.

Further, the air pressure of one of the front right and left wheels maybe estimated on the air pressure of the other of the front wheels, andthe air pressure of one of the rear right and left wheels may beestimated on the air pressure of the other of the rear wheels, since theloads acting on the front right and left wheels are almost equal to eachother, and since the loads acting on the rear right and left wheels arealmost equal to each other, so that the above-indicated relationship isusually satisfied for the two front wheels, and for the two rear wheels.The accuracy of estimation of the air pressure of one of the wheels canbe improved, where the estimation is based on the air pressure ofanother wheel which has the same positional relationship with theabove-indicated one wheel.

The estimation of the air pressure of one wheel based on the detectedair pressure value of another wheel is preferably effected while therunning speed of the vehicle is held within a predetermined range. Whenthe vehicle running speed is higher than the upper limit of thepredetermined range, the accuracy of the estimation may be deteriorated.When the vehicle running speed is lower than the lower limit of therange, the accuracy of detection of the wheel speed sensors 60-66 isrelatively low, so that it is desirable not to use the outputs of thewheel speed sensors 60-66.

The embodiments described above are arranged such that the interval orfrequency of transmission of the wheel-side information from thewheel-side devices 10-16 is held constant. However, the interval oftransmission of the wheel-side information from each wheel-side devicemay be reduced when the rate of change of the air pressure detected bythe air pressure sensor 32 is higher than a predetermined thresholdvalue. In this case, the interval of reception of the wheel-sideinformation by the body-side device 18 is made equal to the reducedinterval of transmission of the wheel-side devices 10-16.

Further, the wheel-side information may be transmitted from thewheel-side devices 10-16 only while the rate of change of the airpressure detected by the air pressure sensor 32 is higher than apredetermined threshold value. Namely, the wheel-side information maynot be transmitted while the rate of change of the detected air pressureis lower than the threshold value. While the rate of change is lowerthan the threshold value, the estimated-air-pressure information isdetermined as the air-pressure information.

Alternatively, the information indicative of the detected air pressureis transmitted while the rate of change of the detected air pressure ishigher than a threshold value, but the information as to whether thedetected air pressure is normal or abnormal is transmitted while therate of change is lower than the threshold value.

In the modified arrangements described above, the rate of reduction ofthe electric energy stored in the battery 58 of each wheel-side device10-16 can be reduced, so that the service life of the battery 58 can beprolonged.

Further, the wheel-side devices and the body-side device may be arrangedso as to permit bi-directional radio or wireless communicationtherebetween. A wheel-state obtaining apparatus illustrated in FIG. 15is an example of this modification. In this apparatus, each of thewheel-side devices 10 b-16 b includes a transmitter/receiver antenna 36b, while the body-side device 18 b includes four transmitter/receiverantennas 20 b-26 b. Each wheel-side device 10 b-16 b further includesthe above-indicated air-pressure-information generating device 34, and atransmission control device 75, while the air-pressure-informationobtaining device 28 b of the body-side device 18 b includes atransmission-state-control-information generating portion 76 in additionto the above-indicated reception processing portion 52, estimatingportion 54, wheel-information determining portion 55, indicator-devicecontrol portion 56 and memory 58. To the air-pressure-informationobtaining device 28 b, there are connected a running-speed sensor 78, ayaw rate sensor 79, a brake-pedal switch 80 and an accelerator-pedalswitch 81 as well as the above-indicated wheel speed sensors 60-66. Thesensors 78, 79 and switches 80, 81 are connected to the obtaining device28 b through signal lines 82. At least one of the sensors and switches78-81 constitutes a vehicle-running-state detecting device 83 operableto detect the running state of the vehicle.

While the brake-pedal switch 80 is in the ON state, it is determinedthat the vehicle is being braked. While the accelerator-pedal switch 81is in the ON state, it is determined that the vehicle is beingaccelerated. While the absolute value of the output of the yaw ratesensor 79 is higher than a predetermined threshold, it is determinedthat the vehicle is turning or cornering. The running speed of thevehicle is detected by the running-speed sensor 78, and the slippingstate of each wheel is obtained on the basis of the detected vehiclerunning speed and the speed of each wheel detected by the wheel speedsensor 60-66.

In the present embodiment of FIG. 15, one of the estimated-air-pressureinformation and the detected-air-pressure information is determined asthe air-pressure information, depending upon the detected running stateof the vehicle. Further, transmission-state control information isgenerated by the transmission-state-control-information generatingdevice 76, on the basis of the detected vehicle running state, and istransmitted to the wheel-side devices 10 b-16 b through the respectivetransmitter/receiver antennas 20 b-26 b, so that the transmissioncontrol device 75 of each wheel-side device 10 b-16 b controls at leastone of the state and amount of transmission of the wheel-sideinformation, according to the received transmission-state controlinformation.

When it is determined on the basis of the detected vehicle running statethat the accuracy of estimation of the air pressure by the estimatingportion 54 is higher than a predetermined limit, theestimated-air-pressure information obtained by the estimating portion 54is determined as the air-pressure information. When it is determinedthat the accuracy of estimation is lower than the lower limit, thedetected-air-pressure information obtained by the reception processingportion 52 is determined as the air-pressure information. Further, theestimated-air-pressure information is obtained according to a selectedone of two estimating rules.

One of the estimating rules utilizes a relationship between the tire airpressures of two wheels and the rotating speeds (angular velocities) ofthe two wheels. According to this estimating rule, the air pressure ofone of two wheels is estimated on the basis of the ratio of the detectedspeeds of the two wheels and the detected air pressure of the otherwheel. This rule will be referred to as “a first estimating rule”, andthe estimated-air-pressure information obtained according to this firstestimating rule (rule based on the wheel radius under a dynamic load)will be referred to as “first estimated-air-pressure information”.

The other estimating rule utilizes a relationship between the rate ofchange of the spring constant of the tire of each wheel and the rate ofchange of the tire air pressure. According to this rule, the airpressure of the wheel in question is estimated on the basis of aplurality of sets of speed data of that wheel. This rule will bereferred to as “a second estimating rule”, and theestimated-air-pressure information obtained according to this secondestimating rule (rule based on the resonance frequency, or ruleutilizing an external-disturbance observer) will be referred to as“second estimated-air-pressure information”.

In the present embodiment, it is determined that the accuracy ofestimation of the air pressure is higher than the lower limit, while thevehicle running speed is held within the predetermined range and whilethe wheel speeds are not likely to be influenced by any factors otherthan the tire air pressure. While the vehicle running speed is higherthan a given upper limit, it is known that the accuracy of estimationaccording to the first or second estimating rule is not sufficientlyhigh. Where the wheel speed sensors 60-66 are of an electromagneticpickup type, the accuracy of detection of the wheel speeds by thosesensors is considerably low when the vehicle running speed is lower thana given lower limit, so that it is not desirable to use the wheel speedsrepresented by the outputs of the wheel speed sensors in this condition.It is not adequate to estimate the air pressure of each wheel on thebasis of the wheel speed during running of the vehicle on a bad roadwayor during excessive slipping of the wheel on the roadway surface (in anexcessively locking state of the wheel), because the wheel speed has alarge amount of fluctuation or variation due to the bad roadway surfaceor slipping or locking of the wheel.

Where the air pressure is estimated according to the first estimatingrule, the loads acting on the two wheels (including the wheel whose airpressure is estimated) are required to be substantially equal to eachother, since the angular velocities of the two wheels may vary dependingupon the loads acting on the wheels.

With the above-indicated factors taken into account, the presentembodiment is arranged to use the estimated-air-pressure informationwhen all of the following three conditions are satisfied: (1) Thevehicle is not running on a bad roadway; (2) The vehicle running speedis within a predetermined range; and (3) The amount of slipping of thewheel is not larger than a predetermined upper limit. If at least one ofthose three conditions is not satisfied, the detected-air-pressureinformation is used. Further, the first estimated-air-pressureinformation is obtained when all of the following three conditions aresatisfied: (a) The vehicle is not turning; (b) The vehicle is not beingbraked (with an operation of the brake pedal); and (c) The vehicle isnot being accelerated (with an operation of the accelerator pedal). Ifat least one of those three conditions (a)-(c) is not satisfied, thesecond estimated-air-pressure information is obtained.

The excessively slipping tendency or locking tendency of the wheels canbe detected on the basis of the outputs of the wheel speed sensors60-66.

As described above, the ON state of the brake-pedal switch 82 indicatesthat the vehicle is being braked, and the ON state of theaccelerator-pedal switch 81 indicates that the vehicle is beingaccelerated. The absolute value of the output of the yaw rate sensor 70higher than the predetermined upper limit indicates that the vehicle isturning.

The estimating portion 54 is arranged to execute anestimated-information obtaining program illustrated in the flow chart ofFIG. 16.

This program is initiated with step S151 to determine whether thepresent point of time is the predetermined timing of calculation of theestimated air pressure. If a negative decision (NO) is obtained in stepS151, the control flow goes to steps S152 and S153 to read the rotatingspeeds of the wheels and store then in the memory 58. If an affirmativedecision (YES) is obtained in step S151, the control flow goes to stepsS154-S158 to make the determination as to whether the vehicle is runningon a bad roadway, the determination as to whether the vehicle runningspeed is held within the predetermined range, the determination as towhether the amount of slipping of any wheel is larger than the upperlimit, the determination as to whether the vehicle is turning, and thedetermination as to whether the vehicle is braking braked oraccelerated.

If an affirmative decision (YES) is obtained in step S154 or S156, or ifa negative decision (NO) is obtained in step S155, the control flow goesto step S159 in which the reception processing portion 52 is suppliedwith information which permits the use or determination of thedetected-air-pressure information as the air-pressure information. If anegative decision (NO) is obtained in both of steps S154 and S156 and ifan affirmative decision (YES) is obtained in step S155, the control flowgoes to step S157-S163 to obtain the first or secondestimated-air-pressure information, depending upon whether the vehicleis turning and whether the vehicle is being braked or driven.

The turning, braking or acceleration of the vehicle has a relativelysmall influence on the accuracy of estimation of the air pressureaccording to the second estimating rule, but has a relatively largeinfluence on the accuracy of estimation according to the firstestimating rule. In view of this fact, the air pressure of the wheel inquestion is estimated according to the second estimating rule duringrunning, braking or acceleration of the vehicle, and according to thefirst estimating rule in the other running state of the vehicle.

If an affirmative decision (YES) is obtained in step S157 or S158, thecontrol flow goes to steps S160 and S161 to supply the receptionprocessing portion 54 with information to use the secondestimated-air-pressure information as the air-pressure information, andto obtain the second estimated-air-pressure information according to thesecond estimating rule, that is, according to a program illustrated inthe flow chart of FIG. 17, which is executed by a second estimatingportion 54 b of the estimating portion 54. Namely, step S161 a isimplemented to obtain the second estimated-air-pressure informationrepresentative of a second estimated value (corresponding to theprovisional estimated value in the first embodiment of FIG. 1) on thebasis of a plurality of sets of speed data of the wheel in questionstored in the memory 58. Step S161 a is followed by step S161 b tosupply the indicator-device control portion 56 with the obtained secondestimated-air-pressure information as the air-pressure information. StepS161 c is then implemented to clear the memory 58.

If a negative decision (NO) is obtained in step S157 or S158, thecontrol flow goes to steps S162 and S163 to supply the receptionprocessing portion 52 with information to use the firstestimated-air-pressure information as the air-pressure information, andto obtain the first estimated-air-pressure information according to thefirst estimating rule, that is, according to a program illustrated inthe flow chart of FIG. 18, which is executed by a first estimatingportion 54 a of the estimating portion 54. Namely, step S163 a isimplemented to read the detected air pressure values received from thereception processing portion 52. Step S163 a is followed by step S163 bto obtain the ratio of the rotating speeds of the two wheels inquestion. Then, step S163 c is implemented to obtain the firstestimated-air-pressure information on the basis of the obtained ratio.Then, the control flow goes to step S163 d to supply theindicator-control portion 56 with information to use the thus obtainedfirst estimated-air-pressure information as the air-pressureinformation, and to step S163 e to clear the memory 58. In step S163 c,the air pressure of one wheel is estimated as in the embodiment of FIG.12, or the air pressure values of two or more wheels are estimated inthe embodiment of FIG. 14. Step S163 a may be formulated to read the airpressure value or values of the wheel or wheels selected to estimate theair pressure value of the wheel in question, or to read the lastdetected air pressure value.

The reception processing portion 52 is arranged to execute adetected-information obtaining program illustrated in the flow chart ofFIG. 19. The program is initiated with step S171 to determine whetherthe wheel-side information has been received by the correspondingreceiver antenna. If an affirmative decision (YES) is obtained in stepS171, the control flow goes to step S172 to process the receivedwheel-side information and extract the air-pressure value. Step S172 isfollowed by step S173 to determine whether the information permittingthe use or determination of the detected-air-pressure information as theair-pressure information has been received. If an affirmative decision(YES) is obtained in step S173, the control flow goes to step S174 tosupply the indicator-device control portion 5 with thedetected-air-pressure information as the air-pressure information, andthen to step S175 to transmit transmission-state-control informationsuch as transmission-permitting information and short-intervaltransmission information to the wheel-side devices through thetransmitter/receiver antennas 20 b-26 b.

If a negative decision (NO) is obtained in step S173, the control flowgoes to step S176 to determine whether the information to use the secondestimated-air-pressure information has been received. If an affirmativedecision (YES) is obtained in step S176, the control flow goes to stepS177 to transmit transmission-inhibiting information to all of thewheel-side devices 10 b-16 b through the transmitter/receiver antennas20 b-26 b. If a negative decision (NO) is obtained in step S176, thecontrol flow goes to step S178 to transmit the transmission-permittinginformation to all of the wheel-side devices 10 b-16 b through thetransmitter/receiver antennas 20 b-26 b, and then to step S179 to supplythe estimating portion 54 with the detected-air-pressure information.

Steps S176-S179 may be implemented when the wheel-side information hasnot been received, that is, when a negative decision (NO) is obtained instep S171.

Each of the wheel-side devices 10 b-16 b is arranged to execute atransmission-control program illustrated in the flow chart of FIG. 20.The program is initiated with step S181 to determine whether thetransmission-state-control information has been received by thetransmitter/receiver antenna 26 b. If an affirmative decision (YES) isobtained in step S181, the control flow goes to step S182 to determinewhether the transmission-inhibiting information has been received. If anaffirmative decision (YES) is obtained in step S182, the control flowgoes to step S183 to inhibit the transmission of the wheel-sideinformation through the transmitter/receiver antenna 36 b. In this case,the detection of the air pressure of the corresponding wheel and thegeneration of the wheel-side information may also be inhibited. However,this inhibition is not essential.

If a negative decision (NO) is obtained in step S182, this means thatthe received transmission-state-control information includes thetransmission-permitting information. In this case, the control flow goesto step S184 to determine whether the receivedtransmission-state-control information includes the short-intervaltransmission information. If an affirmative decision (YES) is obtainedin step S184, the control flow goes to step S185 to shorten thetransmission interval of the wheel-side device 10 b-16 b. If a negativedecision (NO) is obtained in step S184, the transmission at the normaltransmission interval is permitted.

As described above, the transmission of the wheel-side information fromthe wheel-side device 10 b-16 b is inhibited when theestimated-air-pressure information is used as the air-pressureinformation, so that the electric energy stored in the battery 38 can besaved, resulting in a prolonged service life of the battery 38. In thepresent embodiment of FIGS. 15-20, the reception processing portion 52functions as a detected-air-pressure information obtaining portionoperable to obtain the detected-air-pressure information, and atransmission-state-control-information transmitting portion operable totransmit the transmission-state-control information to the wheel-sidedevices 10 b-16 b.

In the present embodiment, it is not essential that one of the firstestimated-air-pressure information and the second estimated-air-pressureinformation is obtained as the estimated-air-pressure information,depending upon the running state of the vehicle. Namely, the embodimentmay be arranged such that one of the estimated-air-pressure informationand the detected-air-pressure information is used as the air-pressureinformation.

Where one of the second estimated-air-pressure information and thedetected-air-pressure information is used as the air-pressureinformation, steps S157, S158, S160, S162, S163, S176, S178 and S179 arenot necessary. Where one of the first estimated-air-pressure informationand the detected-air-pressure information is used as the air-pressureinformation, the detected-air-pressure information is used when theaffirmative decision (YES) is obtained in steps S157 and S158. That is,step S159 is implemented when the affirmative decision is obtained insteps S157 and S158. In this case, steps S150, S161, S162, S176 and S177are not necessary, and the transmission of the transmission-permittinginformation to the wheel-side device 10 b-16 b is not essential.

Further, the body-side device 18 b may be arranged to transmit to thewheel-side devices 10 b-16 b transmission-requesting informationrequesting the transmission of the wheel-side information, so that thewheel-side devices 10 b-16 b transmit the wheel-side information to thebody-side device 18 b, in response to the transmission-requestinginformation.

In the embodiments of FIGS. 15-20, one of the estimated-air-pressureinformation and the detected-air-pressure information is used ordetermined as the air-pressure information, depending upon whether thevehicle is running on a bad roadway, whether the vehicle running speedis held within the predetermined range, and whether the amount ofslipping of any wheel is larger than the upper limit. However, thisarrangement is not essential. For example, one of theestimated-air-pressure information and the detected-air-pressureinformation may be used depending upon one or two of the above-indicatedthree conditions, or depending upon any other conditions, or dependingupon the above-indicated three conditions and any other additionalcondition or conditions.

Further, one of the detected-air-pressure information and theestimated-air-pressure information may be used depending upon the stateof change of the estimated air pressure value of the wheel in question.

For instance, the estimating portion 54 is arranged to execute anestimated-information obtaining program illustrated in the flow chart ofFIG. 21. This program is initiated with step S181 to determine whetherthe present point of time is the predetermined timing of calculation ofthe estimated air pressure value. If an affirmative decision (YES) isobtained in step S181, the control flow goes to step S201 to estimatethe air pressure value P′i of the wheel in question on the basis of aplurality of speed values of the wheel stored in the memory 58, and thento step S202 to determine whether an absolute value of an amount ofchange ΔP′i of the estimated air pressure value (a difference betweenthe air pressure values estimated in the last and present cycles ofexecution of the program) is larger than a predetermined value ΔPa. If anegative decision (NO) is obtained in step S202, the control flow goesto step S203 to determine the estimated-air-pressure information as theair-pressure information, and supply the indicator-device controlportion 56 with the estimated-air-pressure information. Step S203 isfollowed by step S204 to supply the reception processing portion 52 withthe information inhibiting the use of the detected-air-pressureinformation. If an affirmative decision (YES) is obtained in step S202,the control flow goes to step S205 to supply the reception processingportion 52 with the information permitting the use of thedetected-air-pressure information.

On the other hand, the reception processing portion 52 is arranged toexecute a detected-information obtaining program illustrated in the flowchart of FIG. 22. This program is initiated with step S211 to determinewhether the information permitting the use of the detected-air-pressureinformation has been received. If an affirmative decision (YES) isobtained in step S212, the control flow goes to step S212 to transmitthe transmission-permitting information to the wheel-side device 10 b-16b through the transmitter/receiver antenna 20 b-26 b. Step S212 isfollowed by step S213 to determine whether the wheel-side informationhas been received. If an affirmative decision (YES) is obtained in stepS213, the control flow goes to step S214 to process the receivedwheel-side information, and to step S215 to supply the indicator-devicecontrol portion 56 with the detected-air-pressure information as theair-pressure information.

If the information inhibiting the use of the detected-air-pressureinformation, rather than the information permitting the use, has beenreceived, a negative decision (NO) is obtained in step S211, and thecontrol flow goes to step S216 to transmit the transmission-inhibitinginformation to the wheel-side device 10 b-16 b, so that the wheel-sideinformation is not transmitted to the reception processing portion 52.

In the present embodiment, the detected-air-pressure information isdetermined as the air-pressure information when the absolute value ofthe amount of change of the estimated air pressure value (provisionalestimated value) is larger than the predetermined value. This is becausethe detected-air-pressure information more accurately represents theactual air pressure when the absolute value of the amount of change ofthe estimated air pressure value is larger than the predetermined value.The estimated-air-pressure information is obtained for each of thewheels, and the determination as to whether the estimated-air-pressureinformation or the detected-air-pressure information should be used iseffected for each of the wheels whose air pressure values have beenestimated. Accordingly, the transmission-permitting information or thetransmission-inhibiting information is transmitted from thetransmitter/receiver antenna 20 b-26 b corresponding to each wheel. Inthe present embodiment, it is possible that the detected-air-pressureinformation is used for some of the wheels, while theestimated-air-pressure information is used for the other wheel orwheels.

While the preceding embodiments described above are basically arrangedso as to determine or use one of the estimated-air-pressure informationand the detected-air-pressure information as the air-pressureinformation, the present invention is not limited to the details ofthose embodiments. For example, the estimated-air-pressure informationand the detected-air-pressure information may be alternately used, orthe estimated-air-pressure information or detected-air-pressureinformation which has been once used is repeatedly used for two or morecycles of execution of the program. Further, it is possible to diagnosethe devices provided to obtain the detected-air-pressure information,and the devices provided to obtain the estimated-air-pressureinformation, and use the detected-air-pressure information orestimated-air-pressure information which is obtained by the deviceswhich have been diagnosed to be normal. If the devices to obtain thedetected-air-pressure information and the devices to obtain theestimated-air-pressure information are both normal, it is preferable touse the detected-air-pressure information, which usually represents theactual air pressure value more accurately.

In the embodiments described above, the indicator device 70 iscontrolled according to the air-pressure information obtained by theair-pressure-information obtaining device 28.

However, the wheel-state obtaining apparatus of the present invention isnot limited to this arrangement. For instance, the tire air pressure ofeach wheel may be adjusted such that the tire air pressure representedby the air-pressure information obtained by the air-pressure-informationobtaining device 28 is held within a predetermined optimum range. Anexample of this modification is shown in FIG. 23, wherein anair-pressure adjusting apparatus 100 is connected to theair-pressure-information obtaining device 28. The air-pressure adjustingapparatus 100 includes an air pressure source 102 operable to apply apressurized air to the tires 31, a valve device 104 operable to controlthe pressure of the pressurized air to be applied to the tires 31, and avalve control portion 106 operable to control the valve device 104 foradjusting the air pressure in each tire 31.

The air-pressure-information obtaining device 28 is arranged to supplythe air-pressure adjusting apparatus 10 with the obtained air-pressureinformation, so that the valve control portion 106 controls the valvedevice 104 such that the air pressure value represented by theair-pressure information is held within the predetermined optimum range.The air-pressure adjusting apparatus 100 is supplied with either thedetected-air-pressure information or the estimated-air-pressureinformation. Since the air-pressure-information obtaining device 28 isarranged to obtain the estimated-air-pressure information even when thedetected-air-pressure information cannot be obtained, the air-pressureadjusting apparatus 100 can be supplied with the air-pressureinformation at least at the predetermined timing of reception of thewheel-side information by the device 28. Where theair-pressure-information obtaining device 28 is arranged to obtain theestimated-air-pressure information during the period (ΔT1 indicated inFIG. 4) of reception of the wheel-side information (between the adjacentmoments of reception of the wheel-side information), the air-pressureadjusting apparatus 100 can be supplied with the air-pressureinformation at a time interval shorter than the reception interval ofthe wheel-side information, so that the actual tire air pressure can bemore intricately controlled by the apparatus 100.

Further, the air-pressure information obtained by theair-pressure-information obtaining device 28 may be used to control anyother devices of the vehicle, such as a suspension system, a steeringsystem, a braking system, a vehicle drive system and a powertransmission system. An example of this modification is shown in FIG.24, wherein a vehicle control apparatus 120 is connected to theair-pressure-information obtaining device 28. The vehicle controlapparatus 120 includes a control actuator portion 122, and an actuatorcontrol portion 124 which is principally constituted by a computer. Thevehicle control apparatus 120 is arranged to receive output signals ofvarious sensors and switches, which do not directly relate to theprevent invention and will not be further described.

The vehicle control apparatus 120 uses the air-pressure information as amain control input under some condition, or as an auxiliary controlinput under some other condition. In the former case, a control targetvalue is directly determined by the air pressure value of each wheelrepresented by the air-pressure information. In the latter case, thecontrol target value is determined by the main control input such as avehicle running state, and the thus determined control target value iscompensated or changed by the air pressure value used as the auxiliarycontrol input, or a threshold value used to initiate the control or acontrol rule is changed on the basis of the air pressure value.

For example, the air pressure value is used as the main control input tocontrol the suspension system of the vehicle such that the vehicle floorlevel is elevated or the damping effect of the shock absorbers isincreased, when the air pressure is lower than a predeterminedthreshold. The air pressure value is also used as the main control inputto control the rear steering angle of a rear steering system of thevehicle, so as to reduce a yaw moment which arises from a difference inthe tire air pressure between the right and left tires. In these cases,the vehicle control apparatus 120 is a suspension control apparatus or arear-steering-angle control apparatus, and the actuator portion 122 is afloor-level adjusting actuator, a shock-absorber damping-effectadjusting valve device or a rear-steering-angle adjusting actuator,while the actuator control portion 124 is a floor-level control unit(electronic control unit: ECU), a damping-effect control unit(suspension control ECU) or a rear-steering-angle control unit (ECU).

For example, the air pressure value is used as the auxiliary controlinput to control the braking system or the rear steering system. In abraking force control to regulate the braking force of each wheel suchthat the actual slip ratio of each wheel coincides with a target value,for instance, the target slip ratio of one of the right and left wheelsthe tire air pressure of which is relatively low is determined to belower than that of the other wheel the tire air pressure of which isrelatively high, so as to reduce the yaw moment of the vehicle whicharises from a higher coefficient of friction between the road surfaceand the right or left tire having the relatively low air pressure, thana coefficient of friction between the road surface and the other tirehaving the relatively high air pressure. In a vehicle stability controlof the braking system to regulate the braking force of each wheel so asto reduce an understeering or oversteering tendency of the vehicleduring turning or cornering of the vehicle, for example, the airpressure value is used to change the moment of initiation of the vehiclestability control, such that the vehicle stability control is initiatedat an earlier point of time for the wheel having a relatively low tireair pressure, than for the wheel having a relatively high tire airpressure, so as to minimize the forces acting on the tires during thevehicle stability control. In the control of the rear steering system todetermine the rear steering angle on the basis of the angle of thesteering wheel and the vehicle running speed, for example, the rate ofchange of the rear steering angle is made lower when the tire airpressures of the rear wheels are relatively low than when the rear tireair pressure are relatively high. This control is effective to preventabrupt application of a large load to the tires having the relativelylow air pressures. The air pressure may also be used to control thevehicle drive system or power transmission system, so as to reduce avehicle drive torque to be applied to the vehicle driving wheels, whenthe tire air pressures of the driving wheels are relatively low. Thiscontrol is effective to reduce the forces acting on the tires of thedriving wheels in the longitudinal direction of the vehicle when the airpressures of the tires are relatively low.

In the above cases, the vehicle control apparatus 120 is a braking-forcecontrol apparatus, a rear-steering-angle control apparatus, adrive-force control apparatus or a power-transmission control apparatus,and the actuator portion 122 is a braking-force control actuator, arear-steering actuator, a driver circuit for a throttle-angle controlvalve or electric motor, or a power-transmission-ratio control valve,while the actuator control portion 124 is a braking-force control unit(ECU), a rear-steering-angle control unit (ECU) or a drive-force controlECU.

In the embodiments described above, the air pressure value is obtainedas the first state of each wheel (one state of the vehicle), and therotating speed of the wheel is obtained as the second state of the wheel(another state of the vehicle). However, the wheel-state obtainingapparatus or vehicle-state obtaining apparatus of this invention may bearranged to obtain any other state of the wheels or the vehicle.

For instance, the wheel-state obtaining apparatus may be arranged toobtain a temperature of the tire of each wheel as the first state of thewheel, or the vehicle-state obtaining apparatus may be arranged toobtain, as states of the vehicle, a load acting on each wheel of thevehicle, a running time or distance of the vehicle after the ignitionswitch is turned ON (from the OFF state to the ON state), and atemperature of the vehicle (ambient temperature). One example of thismodification is shown in FIG. 25.

In the embodiment of FIG. 25, the four wheels are provided withrespective wheel-side devices 200-206, each of which includes atire-temperature sensor 212, a wheel-side-device control device 214, atransmitter antenna 216, and a battery 218. The wheel-side-devicecontrol device 214 includes a tire-information generating device in theform of a temperature-information generating device 219, which isarranged to generate wheel-side information (transmitted information)representative of a tire temperature of each wheel, on the basis of thetire temperature detected by the tire-temperature sensor 212. Thewheel-side information is transmitted to a body-side device 230 throughthe transmitter antenna 216.

The body-side device 230 includes four receiver antennas 240-260corresponding to the respective four wheels, and atemperature-information obtaining device 250. Like theair-pressure-information obtaining device 28 described above, thetemperature-information obtaining device 250 includes a receptionprocessing portion 252, an estimating portion 254, a wheel-informationdetermining portion 255, an indicator-device control portion 256, and amemory 258. To the temperature-information obtaining device 250, thereare connected a running speed sensor 270, load sensors 362-268 operableto detect loads acting on the respective wheels, an ambient-temperaturesensor 270, and an ignition switch 272, through signal lines 273.

The load sensors 262-268 are provided for the respective four wheels,and arranged to detect the loads acting on the wheels, on the basis ofstrains of non-rotary or stationary bodies in the form of suspensionmembers of the vehicle which are located close to the wheels. The loadsensors 262-268 may be provided on the wheels, which are rotary bodies.In this case, the outputs of the load sensors are transmitted to thetemperature-information obtaining device 250 through transmitterantennas. The load acting on each wheel may be estimated on the basis ofthe weight and running state (attitude) of the vehicle. On the basis ofa change in the attitude of the vehicle, an amount of shifting of thevehicle load can be obtained, and the load presently acting on eachwheel can be estimated on the basis of a standard or normal load on thewheel and the obtained amount of shifting of the vehicle load.

The reception processing portion 252 is arranged to extract, from thewheel-side information received by the receiver antennas 240-246, a tiretemperature value detected by the tire temperature sensor 212 for eachwheel, and generate detected-tire-temperature information indicative orrepresentative of the detected tire temperature.

The estimating portion is arranged to estimate the tire temperature ofeach wheel on the basis of the output signals of the ambient temperaturesensor 260, load sensors 262-268 and running speed sensor 260, such thatthe estimated tire temperature increases with an increase in thedetected ambient temperature, in the average load on the tires and inthe total or cumulative running time or distance of the vehicle. Thecumulative running time may be a sum of times after the ignition switch272 is turned from the OFF state to the ON state, and during which thevehicle running speed is higher than a predetermined threshold value.The cumulative running distance is a sum of running times after theignition switch 272 is turned ON.

The wheel-information determining portion 255 is arranged to determineone of the detected-tire-temperature information and theestimated-tire-temperature information as tire-temperature information.In the present embodiment, the detected-tire-temperature information isused as the tire-temperature information when the wheel-side informationhas been received by the receiver antenna 240-246, and theestimated-tire-temperature information is used as the tire-temperatureinformation when the wheel-side information has not been received.

The indicator-device control portion 256 is arranged to determinewhether the tire temperature represented by the tire-temperatureinformation is higher than a predetermined upper limit or not. If thetire temperature is determined to be higher than the upper limit, theindicator-device control portion 256 activates the alarming portion 74of the indicator device 70. As in the preceding embodiments, theindicator device 70 includes the alarming portion 74, and the indicatingportion 72 operable to indicate the detected tire temperatures.

In the embodiment of FIG. 25, the tire-temperature information isobtained at least at the predetermined timing of reception of thewheel-side information, which is short enough to prevent delayedactivation of the alarming portion 74 to indicate that the tire has anexcessively high temperature.

The wheel-information determining portion 255 may be arranged todetermine, in principle, the estimated-tire-temperature information asthe tire-temperature information, and determine thedetected-tire-temperature information as the tire-temperatureinformation only the rate of change of the detected ambient temperatureor the wheel load is higher than a predetermined threshold.

When the vehicle has left a garage or has run into or left a tunnel, theambient temperature of the vehicle may change at a relatively high rate.When the vehicle is running on a bad roadway and the vehicle attitude isconsiderably changing, the wheel loads may change at a relatively highrate. Under these conditions, the tire temperature estimated on thebasis of the changing ambient temperature or wheel load may considerablyfluctuate, depending upon the specific rule of estimation of the tiretemperature. For this reason, it is desirable to use thedetected-tire-temperature information when the rate of change of theambient temperature or wheel load is higher than the predetermined upperlimit.

The determination as to whether the rate of change of the wheel load ishigher than the upper limit may be effected on the basis of the outputsignal of the load sensor 262-268. However, it is possible to determinethat the rate of change of the wheel load is higher than the upperlimit, when it is determined that the vehicle is running on a badroadway.

The estimating portion 254 is arranged to execute anestimated-information obtaining program illustrated in the flow chart ofFIG. 26, while the reception processing portion 252 is arranged toexecute a detected-information obtaining program illustrated in the flowchart of FIG. 27. These programs will be described only briefly, sincethe programs are similar to those described above with respect to thepreceding embodiments.

The estimated-information obtaining program of FIG. 26 executed by theestimating portion 254 is initiated with steps S251 and S252 todetermine whether the amount of change of the ambient temperature isequal to or larger than a predetermined value, and whether the number ofoccurrences within a preset time of a condition in which the absolutevalue of the amount of change of the wheel load is equal to or largerthan a predetermined value is larger than a predetermined thresholdvalue. If a negative decision (NO) is obtained in both steps S251 andS252, the control flow goes to step S253 to determine whether thepresent point of time is the predetermined timing of calculation of theestimated value of the tire temperature. If an affirmative decision(YES) is obtained in step S253, the control flow goes to steps S254 andS255 to estimate the tire temperature of the wheel in question andsupply the indicator-device control portion 256 with theestimated-tire-temperature information as the tire-temperatureinformation. Step S255 is followed by step S256 to supply the receptionprocessing portion 252 with information inhibiting the use of thedetected-tire-temperature information. If an affirmative decision (YES)is obtained in either one of steps S251 and S252, the control flow goesto step S257 to supply the reception processing portion 252 with theinformation permitting the use of the detected-tire-temperatureinformation.

In the detected-information obtaining program in FIG. 27, an affirmativedecision (YES) is obtained in step S263 when the reception processingportion 252 has received from the estimating portion 254 the informationpermitting the use of the detected-tire-temperature information. In thiscase, the control flow goes to step S264 to supply the indicator-devicecontrol portion 256 with the detected-tire-temperature information asthe tire-temperature information.

As described above, the embodiment of FIGS. 25-27 is arranged todetermine or use the detected-tire-temperature information as thetire-temperature information when the accuracy of estimation of theestimated-tire-temperature information is relatively low. Thus, thetire-temperature can be accurately obtained.

The first state of each wheel in the form of the tire temperature of thewheel can be estimated on the basis of the vehicle state in the form ofthe running time or distance of the vehicle after the ignition switch272 has been turned ON. In other words, estimation as to whether thetire has been overheated may be based on the total or cumulative runningtime or distance of the vehicle. More specifically described, it ispossible to estimate that the tire has been overheated, when thecumulative vehicle running time or distance has reached a predeterminedvalue.

The tire temperature may also be estimated on the basis of the rotatingspeed of the wheel, rather than the vehicle running speed. That is, thecumulative running time or distance of the vehicle can be estimated onthe basis of the cumulative peripheral speed of the wheel, so that thetire temperature can be estimated on the basis of the thus estimatedcumulative vehicle running time or distance. Further, the condition inwhich the wheel is braked or accelerated may be detected on the basis ofthe state of change of the rotating speed of the wheel. The tiretemperature of the wheel can be estimated on the basis of the repeatedbraking or accelerating operations of the wheel. It is possible toestimate that the tire temperature is higher where the number ofrepetition of the braking or accelerating operations of the wheel isrelatively large than where the number of repetition is relativelysmall. The braking and accelerating operations may be detected on thebasis of the outputs of a longitudinal acceleration sensor provided todetect the longitudinal acceleration value of the vehicle.

The first state of each wheel may be forces acting on its tire, whilethe state of the vehicle may be braking, accelerating and wheel steeringconditions of the vehicle. An example of this modification isillustrated in FIG. 28.

In the embodiment of FIG. 28, the four wheels are provided withrespective wheel-side devices 300-306, each of which includes a forcesensor 312, a wheel-side-device control device 314, a transmitterantenna 316 and a battery 318. The wheel-side-device control device 314includes a tire-information generating device in the form of aforce-information generating device 319. The force sensor 312 isoperable to detect forces which respectively act on the correspondingtire in the longitudinal, lateral and vertical directions of thevehicle. The force sensor 312 is provided on a rotary body, and includesa plurality of strain detectors. Where the strain detectors consist ofthree strain detectors arranged to be deformed by forces acting thereonin the respective longitudinal, vertical and lateral directions and notto be deformed by other forces, these three strain detectors detectthose forces acting on the tire in the longitudinal, vertical andlateral directions. Where the strain detectors consist of a straindetector arranged to detect a force acting thereon in the lateraldirection of the vehicle, and strain detectors arranged to detect forcesacting thereon in directions parallel to the plane of the wheel, theforces acting on the tire in the longitudinal and vertical directions ofthe vehicle can be detected on the basis of the outputs of the straindetectors and an angle of rotation of the wheel.

The forces acting on the tire in the longitudinal, vertical and lateraldirections detected by the force sensor 312 are received by thewheel-side-device control device 314, and transmitted through thetransmitter antenna 316 to a body side device 330. However, those forcesdetected by the strain detectors of the force sensor 312 may be directlyreceived by the body-side device 330.

The body-side device 330 includes receiver antennas 332-338corresponding to the respective four wheels, and a force-informationobtaining device 340. Like the air-pressure-information obtaining device28, 28 b and the temperature-information obtaining device 250 providedin the preceding embodiments, the force-information obtaining device 340includes a reception processing portion 352, an estimating portion 354,a wheel-information determining portion 355, an indicator-device controlportion 356, and a memory 358. To the force-information obtaining device340, there are connected a driving-state detecting device 360 operableto detect a driving or accelerating state of the vehicle, abraking-state detecting device 362 operable to detect a braking-state ofthe vehicle, and a steering-state detecting device 364 operable todetect a steering-state of the wheels.

The driving-state detecting device 360 includes at least one of adrive-system-state detecting device operable to detect an operatingstate of a vehicle drive system, a power-transmission-system-statedetecting device operable to detect an operating state of a vehiclepower-transmission system, and an accelerator-pedal-state detectingdevice operable to detect an operating state of an accelerating memberin the form of an accelerator pedal. The driving or accelerating stateof the vehicle can be detected on the basis of the detected operatingstate of the vehicle drive system or power-transmission system or theoperating state of the accelerating member. Where the vehicle drivesystem includes an internal combustion engine, the operating state ofthe vehicle drive system may be detected on the basis of the detectedamount of opening of a throttle valve or the detected speed of theengine. Where the vehicle drive system includes an electric motor, theoperating state of the vehicle drive system may be detected on the basisof the detected state of a driver circuit provided to control anelectric current to be applied to the electric motor. The detectedoperating state of the power-transmission system indicates the state inwhich vehicle drive power is transmitted to the drive wheels of thevehicle. The driving state of the vehicle indicates the state in whichthe drive wheels are driven or not.

Where the braking system of the vehicle is arranged to force a frictionmember onto a rotor rotating with each wheel of the vehicle, thebraking-state detecting device 362 includes at least one of a forcedetector operable to detect a braking force with which the frictionmember is forced onto the rotor, and a brake-pedal-state detectingdevice operable to detect an operating state of a brake operating memberin the form of a brake pedal. Where the braking system is hydraulicallyoperated, the braking force can be detected on the basis of a hydraulicpressure applied to activate the friction member. Where the brakingsystem includes an electric motor, the braking force can be detected onthe basis of a force produced by the electric motor. Where the brakingsystem includes a hydraulically operated brake cylinder, thebraking-state detecting device 362 may be arranged to detect thehydraulic pressure in the brake cylinder, or any hydraulic pressureequivalent to the pressure in the brake cylinder, for instance, thepressure in a master cylinder. The braking-state detecting device 362 isarranged to detect the braking state of each wheel.

The steering-state detecting device 364 may include a steering-anglesensor operable to detect the steering angle of the steering wheel ofthe vehicle, and a running-speed detecting device operable to detect therunning speed of the vehicle. Alternatively, the steering-statedetecting device 364 may include a detecting device operable to detectthe operating state of the power steering system of the vehicle, or ayaw rate sensor or a lateral acceleration sensor which is arranged todetect the yaw rate or the lateral acceleration of the vehicle. Thesteering angle, running speed, yaw rate and lateral acceleration valueof the vehicle indicate the state in which the vehicle is turning, andthe steering state of each wheel can be estimated on the state ofturning of the vehicle. The steering-state detecting device 364 may bereferred to as a turning-state detecting device operable to detect thestate of turning of the vehicle.

The reception processing portion 352 is arranged to obtaindetected-force information indicative or representative of the forcesacting on each wheel, on the basis of the wheel-side informationreceived through the receiver antennas 332-338.

The estimating portion 354 is arranged to estimate the forces on thewheel in the longitudinal, lateral and vertical directions, on the basisof the driving state of each drive wheel, the braking state of eachwheel, and the steering state of each wheel.

For example, the force acting on the wheel in the longitudinal directionof the vehicle can be estimated on the basis of the driving state orbraking state of the wheel. Further, a shift of a load on the vehiclemay be estimated by estimating the acceleration or deceleration value ofthe vehicle on the basis of the accelerating or braking state of eachwheel. The amount of the load shift with respect to a predeterminedreference load value is added to the force which acted on the wheel inthe vertical direction and which was detected by the force sensor 312.Thus, the force currently acting on each wheel in the vertical directioncan be estimated. Further, the force acting on each wheel in the lateraldirection may be estimated on the basis of the steering state of thewheel. The amount of the load shift may also be estimated on the basisof outputs of a floor-level sensing device arranged to detect the floorlevel of the vehicle.

While the wheel-state obtaining apparatus may be provided with means forinforming the vehicle operator of the thus estimated vertical,longitudinal and lateral forces acting on each wheel, the provision ofthis means is not essential. For example, the apparatus may be providedwith means for indicating whether the friction coefficient of theroadway surface or the state of turning of the vehicle is highly likelyto reach a critical value or state.

For instance, the friction coefficient of the roadway surface isobtained on the basis of the longitudinal and vertical forces acting oneach other, and the obtained friction coefficient may be indicated onthe indicating portion 72 of the indicator device 70. Theindicator-device control portion 356 may be arranged to determinewhether the obtained friction coefficient is lower than a predeterminedlower limit, and activate the indicating portion 72 when the frictioncoefficient is lower than the lower limit, that is, when the roadwaysurface is excessively or extremely slippery.

The indicator-device control portion 356 may be arranged to: obtain atarget value of the lateral force acting on the wheel, on the basis ofthe steering angle of the steering wheel and the vehicle running speedand yaw rate; calculate a difference of a detected or estimated value ofthe lateral force with respect to the obtained target value; determinewhether the difference (=target value−detected or estimated value) issmaller than a predetermined threshold; and if the difference is smallerthan the threshold, activate the indicator device 70 to indicate thatthe difference is smaller than the threshold.

The estimation as to whether the turning state of the vehicle iscritical or not may be effected on the basis of a relationship betweenthe cornering force and the steering angle. The cornering force (forceacting on the wheel in a direction perpendicular to the runningdirection of the vehicle) can be obtained on the basis of the lateralforce acting on the wheel in a direction perpendicular to thelongitudinal direction of the vehicle, and the steering angle. When therate of increase of the cornering force is lower than the rate ofincrease of the steering angle, the turning state of the vehicle is morecritical than when the former is higher than the latter.

Further, cornering power may be obtained on the basis of the corneringforce and the steering angle, and a self-aligning torque may be obtainedon the basis of the lateral force, friction force and lateral slippingangle of the wheel. The lateral slipping angle is considered to be heldsubstantially equal to the steering angle before the turning state ofthe vehicle has become critical.

The wheel-information determining portion 355 is arranged to determinethe detected-force information as tire-force information when thewheel-side information has been received by the receiver antenna332-338, and determine estimated-force information as the tire-forceinformation when the wheel-side information has not been received.

Thus, the force-information obtaining device 340 obtains the tire-forceinformation indicative or representative of the forces acting on thetire of each wheel at the predetermined timing of reception of thewheel-side information, making it possible to regularly inform thevehicle operator of the necessary information.

The wheel-information determining portion 355 may be arranged to inhibitthe use of the estimated-force information when the amount of slippingor locking of each wheel in the longitudinal or lateral direction islarger than a predetermined threshold, since the accuracy of estimationof the estimated-force information is low in such slipping or lockingstate of the wheel. When the braking system or drive system is inoperation to effect an anti-lock, traction or vehicle stability control,the wheel-information determining portion 355 may be arranged to alsoinhibit the use of the estimated-force information during the anti-lock,traction or vehicle stability control. The force sensor 312 and theforce-information obtaining device 340 need not be arranged to detect orobtain all of the forces acting on each wheel in the above-indicatedthree directions, and may be arranged to detect or obtain at least oneof the three forces in the respective longitudinal, vertical and lateraldirections.

To the force-information obtaining device 340, there are connected thevehicle control apparatus 120, which includes the actuator portion 122and the actuator control portion 124, as described above with respect tothe embodiment of FIG. 24. The vehicle control device apparatus 120 issupplied with the detected-force information or the estimated-forceinformation.

The vehicle control apparatus 120 is arranged to control the state ofthe vehicle, on the basis of the longitudinal, vertical and lateralforces acting on each wheel (tire). In this case, too, the forces of thewheels are used as a main control input under some conditions, or anauxiliary control input under some other conditions.

For example, the actuator portion 122 of the vehicle control apparatus120 may be a braking-force control actuator which is controlled tocontrol the braking force to be applied to each wheel such that thelongitudinal force acting on each wheel under braking coincides with atarget value. Alternatively, the actuator portion 122 may be arear-steering actuator which is controlled to control the rear steeringsystem such that the lateral force acting on each wheel during turningof the vehicle coincides with a target value.

The control rule used for the anti-lock braking control of each wheelmay be changed depending upon the friction coefficient of the roadwaysurface as estimated on the basis of the vertical and longitudinalforces of the wheel. Namely, the rate of increase in the brakingpressure applied to the wheel is made higher when the frictioncoefficient is relatively high, and the rate of reduction in the brakingpressure is made higher when the friction coefficient is relatively low.

In each of the preceding embodiments, the wheel-side informationrepresentative of the state of each wheel is transmitted in a wirelessfashion or by radio or wireless communication, and the wheel state isdetected by the device disposed on the rotary member in the form of thewheel. However, this wheel-state detecting device may be disposed on astationary member, rather than a rotary member such as the wheel. Evenwhere the detecting device is disposed on the stationary member, thewheel-side information may be transmitted by radio communication, if itis difficult to connect the detecting device and information-processingor obtaining device of the body-side device by signal lines. An exampleof this modification is shown in FIG. 29.

A vehicle-state obtaining apparatus shown in FIG. 29 includes fourremote detecting devices 400 a-400 d, a remote-information obtainingdevice 402, a wire-transmission-dependent-information obtaining device404, and an information-processing device 406. The remote detectingdevices 400 a-400 d are provided for the respective four wheels, andarranged to detect braking torques applied to the respective wheels.These remote detecting devices 400 a-400 d are not disposed on rotarymembers, but are disposed on stationary members in the form of brakecalipers, which are unsprung members of the vehicle.

Each of the remote detecting devices 400 a-400 d includes a firstdetecting device in the form of a braking-torque sensor 412, asensor-information generating device 414, a transmitter antenna 416, anda battery 418. The sensor-information generating device 414 is arrangedto generate sensor information on the basis of the output of thebraking-torque sensor 412, and the generated sensor information istransmitted through the transmitter antenna 416. The sensor informationindicates or represents the braking torque as detected by thebraking-torque sensor 412.

The information-processing device 406 includes four receiver antennas419 a-419 d corresponding to the respective wheels, a receptionprocessing portion 424, an estimating portion 426 and aninformation-determining portion 428. To the estimating portion 426,there is connected through a signal line 422 a second detecting devicein the form of a master-cylinder pressure sensor 420. Theinformation-processing device 406 is disposed on a sprung member of thevehicle.

The reception processing portion 424 is arranged to obtain remoteinformation indicative of the braking torque values, on the basis of theinformation received by the receiver antennas 419 a-410 d. The receiverantennas 419 a-419 d and the reception processing portion 424 constitutea major part of the remote-information obtaining device 402.

The estimating portion 416 is arranged to estimate the braking force ofeach wheel on the basis of the sensor information which represents themaster cylinder pressure and which is received through the signal line422, and obtain wire-transmission-dependent information representativeof the estimated braking torque. Thewire-transmission-dependent-information obtaining device 404 isconstituted by the master-cylinder-pressure sensor 420, signal line 422and estimating portion 416.

The information-determining portion 428 is arranged to determine, asbraking-torque information, one of the remote information representativeof the detected braking torque and the wire-transmission-basedinformation representative of the estimated braking torque. For example,the information-determining portion 428 determines the remoteinformation as the braking-torque information when the information hasbeen received through the receiver antenna 419 a-419 d, and determinethe wire-transmission-dependent information as the braking-torqueinformation when the information has not been received through thereceiver antenna 419 a-419 d. Further, the information-determiningportion 428 determines the remote information as the braking-torqueinformation when the amount of slipping of the wheel under braking isrelatively large, and determines the wire-transmission-dependentinformation as the braking-torque information when the amount ofslipping of the wheel is relatively small. It is noted that the accuracyof estimation of the braking torque based on the detected mastercylinder pressure is low, when the amount of slipping of the wheel underbraking is relatively large. The indicator device 430 is supplied withthe braking-torque information selected by the information-determiningportion 428.

In the embodiment of FIG. 28, each remote detecting device 400 a-400 dis disposed on the brake caliper and arranged to detect the brakingtorque of the corresponding wheel. However, each remote detecting devicemay be disposed on a stationary member adjacent to the correspondingwheel, and arranged to detect the rotating speed of the wheel. Therotating speed of a driving wheel may be estimated on the basis of therotating sate of the output shaft of a vehicle-drive system, or anoperating state of a power-transmission system. In this case, the remoteinformation representative of the detected wheel speed, or theinformation representative of the wheel speed estimated on the basis ofthe operating state of the vehicle drive system or power-transmissionsystem may be used as wheel-speed information. It is not essentialprovide a plurality of remote detecting devices. Namely, thevehicle-state obtaining apparatus may use only one remote detectingdevice. Further, each remote detecting device need not be arranged todetect the state of the corresponding wheel.

Further, a remote detecting device 500 may be provided on a towedvehicle 502, as shown in FIG. 30. The remote detecting device 500includes a first detecting device 504 arranged to detect the state ofthe towed vehicle 502 (e.g., running speed, wheel rotating speeds,braking forces generated by a braking system), and a transmitter antenna506 operable to transmit information representative of the detectedstate of the towed vehicle 502.

On the other hand, a tractor vehicle 508 is provided with (a) aremote-information obtaining device 514 including an receiver antenna510 and a reception processing portion 512, (b) awire-transmission-dependent-information obtaining device 520 including asecond detecting device 516 arranged to detect the state of the tractorvehicle 508, like the first detecting 502 of the towed vehicle 508, anda tractor-information obtaining portion 518 which is connected through asignal line to the second detecting device 516 and which processes theinformation received from the second detecting device 516, to obtainwire-transmission-dependent information representative of the detectedstate of the tractor vehicle 508, (c) an information determining portion522, and (d) an indicator device 524. The remote-information obtainingdevice 514, the wire-transmission-dependent-information obtaining device520, and the information determining portion 522 constitute a major partof an information processing device 530. In the present embodiment, theinformation determining portion 522 determines, astowed-vehicle-information, one of the remote information representativeof the detected state of the towed vehicle 502 and thewire-transmission-dependent information obtained by thetractor-information obtaining portion 518. In this case, both of theremote information and the wire-transmission-dependent information aredetected information representative of the states of the towed vehicle502 and the tractor vehicle 508. Namely, the state of the tractorvehicle 508 is considered to represent the state of the towed vehicle502, and is used to estimate the state of the towed vehicle 502.

It will be understood that the present invention may be embodied withvarious other changes, modifications and improvements, such as thosedescribed in the DISCLOSURE OF THE INVENTION, which may occur to thoseskilled in the art.

1-48. (canceled) 49-96. (canceled)
 97. A wheel-state obtaining apparatuscomprising: a wheel-side device provided for each of at least one of aplurality of wheels of a vehicle and including a first-wheel-statedetecting device operable to detect a first state of the correspondingwheel; and a body-side device disposed on a body of the vehicle andincluding (a) a detected-information obtaining device operable to obtaindetected information representative of the first state of saidcorresponding wheel detected by said first-wheel-state detecting device,(b) a vehicle-state detecting device operable to detect a state of thevehicle, (c) an estimated-information obtaining device operable toestimate said first state of said corresponding wheel on the basis of atleast the state of the vehicle detected by said vehicle-state detectingdevice, and obtain estimated information representative of the estimatedfirst state, and (d) a determining device operable to determine one ofsaid detected information and said estimated information, as wheel-stateinformation representative of said first state of said correspondingwheel, and wherein said estimated-information obtaining device isoperable to obtain said estimated information, during a period betweenadjacent moments of reception by said body-side device of wheel-sideinformation representative of said first state of said correspondingwheel detected by said first-wheel-state detecting device, saiddetermining device including a first determining portion operable todetermine, as said wheel-state information, said estimated informationobtained during said period.
 98. A wheel-state obtaining apparatusaccording to claim 97, wherein said determining device includes anindividually determining portion operable for each of said plurality ofwheels, independently of each other, such that one of said detectedinformation and said estimated information is determined as saidwheel-state information for each of said plurality of wheels.
 99. Awheel-state obtaining apparatus according to claim 97, wherein saiddetermining device includes an overall determining portion operable forall of said plurality of wheels, such that one of said detectedinformation and said estimated information is determined as saidwheel-state information, commonly for all of said plurality of wheels.100. A wheel-state obtaining apparatus according to claim 97, whereinsaid determining device includes a detection-failureestimated-information obtaining portion operable to determine saiddetected information as said wheel-state information when said firststate of said corresponding wheel has been detected by saidfirst-wheel-state detecting device, and determine said estimatedinformation as said wheel-state information when said first state hasnot been detected by said first-wheel-state detecting device.
 101. Awheel-state obtaining apparatus according to claim 97, wherein saidwheel-side device further includes (a) a wheel-side-informationtransmitting device operable to transmit, in a wireless fashion, saidwheel-side information, and (b) an electric power source operable tosupply said wheel-side-information transmitting device and saidfirst-wheel-state detecting device with an electric energy, and saidbody-side device further includes a receiving device operable to receivesaid wheel-side information transmitted from said wheel-side device,said detected-information obtaining device including adetected-information extracting portion operable to extract from saidwheel-side information said detected information representative of thefirst state of said corresponding wheel.
 102. A wheel-state obtainingapparatus according to claim 101, wherein said determining deviceincludes a reception-condition-dependent determining portion operable todetermine one of said detected information and said estimatedinformation as said wheel-state information, on the basis of a conditionof reception of said wheel-side information by said receiving device.103. A wheel-state obtaining apparatus according to claim 101, whereinsaid determining device further includes a second determining portionoperable to determine said estimated information as said wheel-stateinformation when said wheel-side information has not been normallyreceived by said receiving device, due to at least one of an abnormalityof said wheel-side device, an abnormality of said receiving device, anda noise included in said wheel-side information, and determine saiddetected information as said wheel-state information when saidwheel-side information has been normally received by said receivingdevice.
 104. A wheel-state obtaining apparatus according to claim 103,wherein said determining portion determines said estimated informationas said wheel-state information when said wheel-side informationreceived by said receiving device is abnormal, and determines saidestimated information as said wheel-state information when saidwheel-state information received by said receiving device is normal.105. A wheel-state obtaining apparatus according to claim 101, whereinsaid determining device includes a reception-failureestimated-information determining portion operable to determine saidestimated information as said wheel-state information when saidwheel-side information has not been received by said receiving device,at a predetermined timing of reception of said wheel-side information bysaid receiving device.
 106. A wheel-state obtaining apparatus accordingto claim 105, wherein said wheel-side-information transmitting deviceincludes a periodically transmitting portion operable to transmit saidwheel-side information at a predetermined interval of transmission. 107.A wheel-state obtaining apparatus according to claim 101, wherein saidwheel-side-information transmitting device includes a periodicallytransmitting portion operable to transmit said wheel-side information ata predetermined interval of transmission, and said estimated-informationobtaining device is operable to obtain said estimated information duringa predetermined interval of reception of said wheel-side information bysaid receiving device.
 108. A wheel-state obtaining apparatus accordingto claim 101, wherein said determining device includes areception-condition determining portion operable to determine whether aratio of reception of said wheel-side information by said receivingdevice is relatively high or low, and a reception-condition-dependentdetermining portion operable to determine said detected information assaid wheel-state information when said reception-condition determiningportion determines that said ratio of reception is relatively high, anddetermine said estimated information as said wheel-state informationwhen said reception-condition determining portion determines that saidratio of reception is relatively low.
 109. A wheel-state obtainingapparatus according to claim 97, wherein said vehicle-state detectingdevice includes a second-wheel-state detecting device operable to detecta second state of each of at least one of said plurality of wheels, saidsecond state being different from said first state.
 110. A wheel-stateobtaining apparatus according to claim 101, wherein saidestimated-information obtaining device includes a detected-stateestimating portion operable to estimate said first state of saidcorresponding wheel after last reception of said wheel-side informationby said receiving device, on the basis of at least said first state ofsaid corresponding wheel represented by the wheel-side informationreceived last by said receiving device.
 111. A wheel-state obtainingapparatus according to claim 110, wherein said vehicle-state detectingdevice includes a second-wheel-state detecting device operable to detecta second state of each of at least one of said plurality of wheels, saidsecond state being different from said first state, and saiddetected-state estimating portion estimates said first state of saidcorresponding wheel, on the basis of said first state represented by thewheel-side information received last by said receiving device, and saidsecond state detected by said second-wheel-state detecting device. 112.A wheel-state obtaining apparatus according to claim 109, wherein saiddetected-state estimating portion includes an estimating portionoperable to estimate said first state of said corresponding wheel,according to a predetermined rule on the basis of said second state ofeach of said at least one of said plurality of wheels detected by saidsecond-wheel-state detecting device, and a rule-changing portionoperable to change said predetermined rule on the basis of said firststate of said corresponding wheel represented by said detectedinformation which has been extracted by said detected-informationobtaining device from the last received wheel-side information.
 113. Awheel-state obtaining apparatus according to claim 109, wherein saiddetected-state estimating portion includes a provisionally estimatingportion operable to obtain a provisional estimated value of said firststate of said corresponding wheel on the basis of said second state ofeach of said at least one of said plurality of wheels detected by saidsecond-wheel-state detecting device, and an estimated-informationobtaining portion operable to compensate said provisional estimatedvalue of said first state on the basis of said first state representedby said detected information extracted from said wheel-side informationwhich has been received last by said receiving device, saidestimated-information obtaining portion determining the compensatedprovisional estimated value of said first state as said estimatedinformation.
 114. A wheel-state obtaining apparatus according to claim109, wherein said detected-state estimating portion includes aprovisionally estimating portion operable to obtain a provisionalestimated value of said first state of said corresponding wheel on thebasis of said second state of each of said at least one of saidplurality of wheels detected by said second-wheel-state detectingdevice, and a final-estimated-value obtaining portion operable tocompensate said provisional estimated value of said first state on thebasis of a predetermined relationship between said first staterepresented by said detected information extracted from said wheel-sideinformation received last by said receiving device, and the provisionalestimated value obtained at a moment substantially coincident with amoment at which said wheel-side information was received last by saidreceiving device, said final-estimated-value obtaining portiondetermining the compensated provisional estimated value of said firststate as a final estimated value of said first state.
 115. A wheel-stateobtaining apparatus according to claim 97, wherein saidestimated-information obtaining device includes an other-wheel-dependentestimating portion operable to estimate said first state of saidcorresponding wheel on the basis of said first state of at least oneother wheel of said plurality of wheels, for obtaining the estimatedinformation representative of the estimated first state.
 116. Awheel-state obtaining apparatus according to claim 115, wherein saidfirst-wheel-state detecting device is provided for each of at least twowheels of said plurality of wheels, and said vehicle-state detectingdevice includes a second-wheel-state detecting device operable to detecta second state of each of said at least two wheels, which second stateis different from said first state, said other-wheel-dependentestimating portion obtaining said estimated information of one of twowheels of said plurality of wheels, by estimating said first state ofsaid one of said two wheels, on the basis of said second state of saidtwo wheels detected by said second-wheel-state detecting device, andsaid first state of the other of said two wheels detected by saidfirst-wheel-state detecting device.
 117. A wheel-state obtainingapparatus according to claim 97, wherein said vehicle-state detectingdevice includes a second-wheel-state detecting device operable to detecta second state of each of at least one of said plurality of wheels, saidat least one of said plurality of wheels including another wheeldifferent from said corresponding wheel, said second state beingdifferent from said first state, and wherein said estimated-informationobtaining device includes a relation-dependent estimated-informationobtaining portion operable to estimate said first state of saidcorresponding wheel to obtain said estimated information representativeof the estimated first state of said corresponding wheel, on the basisof at least said second state of said another wheel detected by saidsecond-wheel-state detecting device, and on the basis of a predeterminedrelationship between the second states of said corresponding wheel andsaid another wheel.
 118. A wheel-state obtaining apparatus according toclaim 97, wherein said vehicle-state detecting device includes asecond-wheel-state detecting device operable to detect a quantity of asecond state of each of at least two wheels of said plurality of wheels,said at least two wheels including said corresponding wheel, said secondstate being different from said first state, and wherein saidestimated-information obtaining device includes an estimated-informationobtaining portion operable to estimate said first state of saidcorresponding wheel to obtain said estimated information representativeof the estimated first state of said corresponding wheel, on the basisof at least a relationship between the quantity of said second state ofsaid corresponding wheel detected by said second-wheel-state detectingdevice, and an average of the quantities of said second states of saidat least two wheels detected by said second-wheel-state detectingdevice.
 119. A wheel-state obtaining apparatus according to claim 97,wherein said vehicle-state detecting device includes asecond-wheel-state detecting device operable to detect a second state ofsaid corresponding wheel, said second state being different from saidfirst state, and said estimated-information obtaining device includes(a) a first-estimated-information obtaining portion operable to estimatesaid first state of said corresponding wheel on the basis of said firststate of at least one other wheel of said plurality of wheels, to obtainfirst estimated information, and (b) a second-estimated-informationobtaining portion operable to estimate said first state of saidcorresponding wheel on the basis of said second state of saidcorresponding wheel, to obtain second estimated information, and whereinsaid determining device includes a selecting portion operable to selectone of said first estimated information and said second estimatedinformation, when said determining device determines said estimatedinformation as said wheel-state information.
 120. A wheel-stateobtaining apparatus according to claim 97, wherein said determiningdevice includes (a) a vehicle-state detecting portion operable to detecta state of the vehicle, and (b) a vehicle-state-dependent determiningportion operable to determine one of said detected information and saidestimated information as said wheel-state information, on the basis ofthe state of the vehicle detected by said vehicle-state detectingportion.
 121. A wheel-state obtaining apparatus according to claim 120,wherein said vehicle-state detecting portion includes avehicle-running-state detecting device operable to detect a runningstate of the vehicle, and said vehicle-state-dependent determiningportion includes a vehicle-running-state-dependent determining portionoperable to determine one of said detected information and saidestimated information as said wheel-state information, on the basis ofthe running state of the vehicle detected by said vehicle-running-statedetecting portion.
 122. A wheel-state obtaining apparatus according toclaim 97, wherein said determining device includes (a) a roadway-surfacedetecting portion operable to detect a condition of a roadway surface onwhich the vehicle is running, and (b) a roadway-condition-dependentdetermining portion operable to determine one of said detectedinformation and said estimated information as said wheel-stateinformation, on the basis of the condition of said roadway surfacedetected by said roadway-surface detecting portion.
 123. A wheel-stateobtaining apparatus according to claim 97, wherein said determiningdevice further includes a third determining portion operable todetermine said estimated information as said wheel-state information,when a state of change of said estimated information as obtained by saidestimated-information obtaining device is smaller than a predeterminedstate.
 124. A wheel-state obtaining apparatus according to claim 97,wherein said determining device includes an independently determiningportion operable to determine one of said detected information and saidestimated information as said wheel-state information representative ofsaid first state of each of said plurality of wheels, such that saiddetected information is selected as said wheel-state information of atleast one of said plurality of wheels, while said estimated informationis selected as said wheel-state information of the other of saidplurality of wheels.
 125. A wheel-state obtaining apparatus according toclaim 101, wherein said wheel-side device further includes atransmission control device operable to control a state of transmissionof said wheel-side information from said wheel-side-informationtransmitting device.
 126. A wheel-state obtaining apparatus according toclaim 125, wherein said transmission control device includes at leastone of (a) a transmission permitting/inhibiting portion operable topermit or inhibit transmission of said wheel-side information from saidwheel-side-information transmitting device, on the basis of a state ofchange of said first state of said corresponding wheel detected by saidfirst-wheel-state detecting device, and (b) a transmission restrictingportion operable to restrict the transmission of said wheel-sideinformation from said wheel-side-information transmitting device, whenthe change of said first state detected by said first-wheel-statedetecting device is slower than a predetermined threshold.
 127. Awheel-state obtaining apparatus according to claim 125, wherein saidwheel-side device further includes (a) a wheel-side-informationgenerating device operable to generate said wheel-side information onthe basis of said first state of said corresponding wheel detected bysaid first-wheel-state detecting device, and (b) a generating-devicecontrol device operable to control said wheel-side-informationgenerating device on the basis of a state of change of said first statedetected by said first-wheel-state detecting device.
 128. A wheel-stateobtaining apparatus according to claim 125, wherein said body-sidedevice further includes a transmission-state-control-informationgenerating device operable to transmit to said wheel-side devicetransmission-state control information indicative of a state oftransmission of said wheel-side information from saidwheel-side-information transmitting device, and said wheel-side devicefurther includes a body-side-information receiving device operable toreceive information from said body-side device, said transmissioncontrol device controlling said wheel-side-information transmittingdevice according to said transmission-state control information receivedby said body-side-information receiving device.
 129. A wheel-stateobtaining apparatus according to claim 128, whereintransmission-state-control-information transmitting device is operableto transmit to said wheel-side device at least one of (a) informationwhich permits the transmission of said wheel-side information, and (b)information which requires the transmission of said wheel-sideinformation, when an accuracy of said estimated information obtained bysaid estimated-information obtaining device is lower than apredetermined threshold.
 130. A wheel-state obtaining apparatusaccording to claim 97, wherein said first-wheel-state detecting deviceincludes at least one of (a) an air-pressure-state detecting deviceoperable to detect a state of an air pressure in a tire of saidcorresponding wheel, (b) a temperature-state detecting device operableto detect a state of a temperature of said tire, (c) a force-statedetecting device operable to detect a state of forces acting on saidcorresponding wheel, and (d) a rotation-state detecting device operableto detect a state of rotation of said corresponding wheel.
 131. Awheel-state obtaining apparatus according to claim 97, wherein saidfirst-wheel-state detecting device includes an air-pressure-statedetecting device operable to detect a state of an air pressure in a tireof each of at least one of said plurality of wheels, and saidvehicle-state detecting device includes a speed detecting deviceoperable to detect a rotating speed of each of at least one of saidplurality of wheels, said estimated-information obtaining deviceincluding an estimated-air-pressure-information obtaining portionoperable to estimate the air pressure of each of said at least one ofthe plurality of wheels on the basis of the rotating speed detected bysaid speed detecting device, to obtain estimated-air-pressureinformation representative of the estimated air pressure.
 132. Awheel-state obtaining apparatus according to claim 97, wherein saidfirst-wheel-state detecting device includes a temperature-statedetecting device operable to detect a state of a temperature of a tireof each of at least one of said plurality of wheels, and saidvehicle-state detecting device includes a running-time/distancedetecting device operable to detect at least one of a cumulative runningtime and a cumulative running distance of the vehicle, saidestimated-information obtaining device including anestimated-temperature-state-information obtaining portion operable toestimate the state of the temperature of the tire of each of said atleast one of the plurality of wheels, on the basis of at least one ofsaid cumulative running time and distance detected by saidrunning-time/distance detecting device, to obtainestimated-temperature-state information representative of the estimatedstate of the temperature.
 133. A wheel-state obtaining apparatusaccording to claim 97, wherein said first-wheel-state detecting deviceincludes a temperature-state detecting device operable to detect a stateof a temperature of a tire of each of at least one of said plurality ofwheels, and said vehicle-state detecting device includes (a) a loaddetecting device operable to detect a load acting on each of said atleast one of the plurality of wheels, (b) a running-state detectingdevice operable to detect a running state of the vehicle, and (c) anambient-temperature detecting device operable to detect an ambienttemperature of the vehicle, said estimated-information obtaining deviceincluding an estimated-temperature-state-information obtaining portionoperable to estimate the state of the temperature of the tire of each ofsaid at least one of the plurality of wheels, on the basis of thedetected load acting on said each wheel and the detected ambienttemperature and running state of the vehicle, to obtainestimated-temperature-state information representative of the estimatedstate of the temperature.
 134. A wheel-state obtaining apparatusaccording to claim 97, wherein said first-wheel-state detecting deviceincludes a force-detecting device operable to detect at least one forceacting on each of at least one of said plurality of wheels, and saidvehicle-state detecting device includes at least one of (a) adriving-state detecting device operable to detect a driving state of thevehicle, (b) a braking-state detecting device operable to detect abraking state of the vehicle, and (c) a turning-state detecting deviceoperable to detect a turning state of the vehicle, saidestimated-information obtaining device including anestimated-force-information obtaining portion operable to estimate saidat least one force acting on each of said at least one of the pluralityof wheels on the basis of at least one of the detected accelerating,braking and turning states of the vehicle, to obtain estimated-forceinformation representative of the estimated at least one force.
 135. Awheel-state obtaining apparatus comprising: a wheel-side device providedfor each of at least one of a plurality of wheels of a vehicle andincluding (a) a first-wheel-state detecting device operable to detect afirst state of the corresponding wheel, and (b) a wheel-side-informationtransmitting device operable to transmit, in a wireless fashion,wheel-side information representative of said first state of saidcorresponding wheel detected by said first-wheel-state detecting device;and a body-side device disposed on a body of the vehicle and including(c) a receiving device operable to receive said wheel-side informationtransmitted from said wheel-side device, (d) a detected-informationobtaining device operable to obtain received-information representativeof the first state of said corresponding wheel, from said wheel-sideinformation received by said receiving device, (e) a vehicle-statedetecting device operable to detect a state of the vehicle, (f) anestimated-information obtaining device operable to estimate said firstsate of said corresponding wheel, on the basis of at least the state ofthe vehicle detected by said vehicle-state detecting device, and obtainestimated information representative of the estimated first state, and(g) an obtaining-device selecting portion operable to select one of saidestimated-information obtaining device and said detected-informationobtaining device, and wherein said estimated-information obtainingdevice is operable to obtain said estimated information, during a periodbetween adjacent moments of reception by said receiving device ofwheel-side information representative of said first state of saidcorresponding wheel detected by said first-wheel-state detecting device,said obtaining-device selecting portion being operable to select saidestimated-information obtaining device during said period.
 136. Avehicle-state obtaining apparatus comprising: a remote detecting deviceincluding a first detecting device, and a transmitting device operableto transmit, in a wireless fashion, first-detecting-device informationincluding information indicative of an output of said first detectingdevice; and an information processing device including (a) aremote-information obtaining device including a receiving deviceoperable to receive said first-detecting-device information transmittedin a wireless fashion from said remote detecting device, saidremote-information obtaining device being operable to obtain remoteinformation representative of a state of the vehicle, on the basis ofsaid first-detecting-device information received by said receivingdevice, (b) a wire-transmission-dependent-information obtaining deviceincluding a second detecting device and operable to obtainwire-transmission-dependent information representative of said state ofthe vehicle, on the basis of second-detecting-device information whichhas been transmitted from said second detecting device through a signalline and which includes information indicative of an output of saidsecond detecting device, and (c) an information determining deviceoperable to determine one of said wire-transmission-dependentinformation and said remote information, as vehicle-state informationrepresentative of said state of the vehicle, and wherein saidwire-transmission-dependent-information obtaining device is operable toobtain said wire-transmission-dependent information, during a periodbetween adjacent moments of reception of said first-detecting-deviceinformation by said remote-information receiving device, saidinformation determining device being operable to determine, as saidvehicle-state information, said wire-transmission-dependent informationobtained during said period.
 137. A vehicle-state obtaining apparatusaccording to claim 136, wherein said first detecting device is operableto detect one state of said vehicle as said state of the vehicle, whilesaid second detecting device is operable to detect another state of thevehicle which is different from said one state, and saidwire-transmission-dependent-information obtaining device includes anestimating portion operable to estimate said one state of the vehicle onthe basis of said another state of the vehicle detected by said seconddetecting device.
 138. A vehicle state obtaining apparatus according toclaim 136, wherein said remote detecting device is provided on a sprungmember of the vehicle, while said information processing device isprovided on an unsprung member of the vehicle.
 139. A vehicle-stateobtaining apparatus according to claim 136, wherein said remotedetecting device is provided on a wheel of the vehicle.
 140. Avehicle-state obtaining apparatus according to claim 136, wherein saidinformation determining device is operable to determine saidwire-transmission-dependent information as said vehicle-stateinformation, when said remote information has not been received by saidremote-information obtaining device.
 141. A vehicle-state indicatingapparatus comprising: a wheel-state obtaining apparatus as defined inclaim 97; a judging device operable to determine whether said firststate of said corresponding wheel is normal or not; and an indicatordevice operable, when said judging device determines that said firststate of said corresponding wheel is not normal, to provide anindication that said first state is not normal.
 142. A vehicle-statecontrol apparatus comprising: a wheel-state obtaining apparatus asdefined in claim 97; an actuator portion operable to control a state ofthe vehicle; and an actuator control portion operable to control saidactuator portion on the basis of said first state of said correspondingwheel obtained by said wheel-state obtaining apparatus.
 143. Awheel-state control apparatus comprising: a wheel-state obtainingapparatus as defined in claim 97; an actuator portion operable tocontrol said first state of said corresponding wheel; and an actuatorcontrol portion operable to control said actuator portion such that saidfirst state of said corresponding wheel obtained by said wheel-stateobtaining apparatus is held within a predetermined range.